diff --git a/packages/inflekt/__tests__/ves-and-exceptions.test.ts b/packages/inflekt/__tests__/ves-and-exceptions.test.ts
index 889984d..78aa907 100644
--- a/packages/inflekt/__tests__/ves-and-exceptions.test.ts
+++ b/packages/inflekt/__tests__/ves-and-exceptions.test.ts
@@ -139,6 +139,57 @@ describe('singularize: suffix classes the inflection library gets wrong', () =>
   });
 });
 
+describe('singularize: -is and -us words', () => {
+  it('depluralizes coined identifiers whose stem ends in a vowel', () => {
+    // The regression that started this: an "apis" table became "apises",
+    // because every -is/-us word was assumed to be already singular.
+    expect(singularize('apis')).toBe('api');
+    expect(singularize('uris')).toBe('uri');
+    expect(singularize('guis')).toBe('gui');
+    expect(singularize('cpus')).toBe('cpu');
+    expect(singularize('gpus')).toBe('gpu');
+    expect(singularizeLast('ApiSchemas')).toBe('ApiSchema');
+    expect(pluralize(singularize('apis'))).toBe('apis');
+    expect(pluralize(singularize('cpus'))).toBe('cpus');
+  });
+
+  it('leaves the dictionary singulars alone', () => {
+    // "iris" and "apis" have the same shape (a vowel plus "s"), so these are
+    // dictionary facts, not rules — see SINGULAR_EXCEPTIONS.
+    for (const word of [
+      'aegis',
+      'analysis',
+      'anxious',
+      'apparatus',
+      'bus',
+      'cactus',
+      'census',
+      'chassis',
+      'corpus',
+      'genius',
+      'iris',
+      'nucleus',
+      'radius',
+      'status',
+      'tennis',
+      'various',
+      'virus',
+    ]) {
+      expect(singularize(word)).toBe(word);
+    }
+  });
+
+  it('still depluralizes the dictionary plurals of vowel stems', () => {
+    expect(singularize('menus')).toBe('menu');
+    expect(singularize('emus')).toBe('emu');
+    expect(singularize('skis')).toBe('ski');
+    expect(singularize('taxis')).toBe('taxi');
+    expect(singularize('alibis')).toBe('alibi');
+    expect(singularize('statuses')).toBe('status');
+    expect(singularize('irises')).toBe('iris');
+  });
+});
+
 describe('SINGULAR_EXCEPTIONS table', () => {
   it('is applied for every entry', () => {
     for (const [plural, singular] of Object.entries(SINGULAR_EXCEPTIONS)) {
diff --git a/packages/inflekt/scripts/generate-exceptions.ts b/packages/inflekt/scripts/generate-exceptions.ts
index dc3656f..3ddfcca 100644
--- a/packages/inflekt/scripts/generate-exceptions.ts
+++ b/packages/inflekt/scripts/generate-exceptions.ts
@@ -179,6 +179,16 @@ for (const singular of [...exceptions.values()]) {
   }
 }
 
+// Round-trip closure for the singulars that end in "s" (aegis, iris, corpus):
+// their plural takes "-es", and the generic rules read that back one letter
+// short (aegises -> aegise), because "-ses" is only "-sis" for the Greek nouns.
+for (const singular of [...new Set(exceptions.values())]) {
+  if (!singular.endsWith('s')) continue;
+  const plural = pluralize(singular);
+  if (plural === singular || exceptions.has(plural)) continue;
+  if (singularizeByRules(plural) !== singular) exceptions.set(plural, singular);
+}
+
 const entries = [...exceptions.entries()].sort(([a], [b]) => a.localeCompare(b));
 const body = entries.map(([plural, singular]) => `  ${plural}: '${singular}',`).join('\n');
 
diff --git a/packages/inflekt/src/exceptions.ts b/packages/inflekt/src/exceptions.ts
index f7ce4f9..e1247da 100644
--- a/packages/inflekt/src/exceptions.ts
+++ b/packages/inflekt/src/exceptions.ts
@@ -16,46 +16,54 @@
  * pluralization returns the key (see scripts/generate-exceptions.ts).
  */
 export const SINGULAR_EXCEPTIONS: Record<string, string> = {
-  abacis: 'abaci',
+  abacus: 'abacus',
   abases: 'abase',
   abstruses: 'abstruse',
   abuses: 'abuse',
-  acanthis: 'acanthi',
+  acanthus: 'acanthus',
   accouterments: 'accouterments',
   accoutrements: 'accoutrements',
   accuses: 'accuse',
   aches: 'ache',
-  adieus: 'adieu',
   ads: 'ads',
+  aegis: 'aegis',
+  aegises: 'aegis',
   aerobatics: 'aerobatics',
   aeronautics: 'aeronautics',
   afterlives: 'afterlife',
   airwaves: 'airwaves',
   alas: 'alas',
-  alibis: 'alibi',
   alkalies: 'alkali',
-  alkalis: 'alkali',
   alms: 'alms',
   aloes: 'aloe',
-  alumnis: 'alumni',
+  alumnus: 'alumnus',
   always: 'always',
   amanuenses: 'amanuensis',
+  amaryllis: 'amaryllis',
   amaryllises: 'amaryllis',
+  ambergris: 'ambergris',
+  ambergrises: 'ambergris',
   amidships: 'amidships',
   amniocenteses: 'amniocentesis',
   amuses: 'amuse',
-  anis: 'ani',
+  animus: 'animus',
   annals: 'annals',
   anopheles: 'anopheles',
-  antipastis: 'antipasti',
   antipodes: 'antipodes',
-  antis: 'anti',
+  anus: 'anus',
   apices: 'apex',
   apotheoses: 'apotheosis',
+  apparatus: 'apparatus',
   appendices: 'appendix',
+  appendicitis: 'appendicitis',
+  appendicitises: 'appendicitis',
   apropos: 'apropos',
+  arbutus: 'arbutus',
   arrears: 'arrears',
+  arthritis: 'arthritis',
+  arthritises: 'arthritis',
   asbestos: 'asbestos',
+  asparagus: 'asparagus',
   astronautics: 'astronautics',
   astrophysics: 'astrophysics',
   atlas: 'atlas',
@@ -63,113 +71,122 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   avalanches: 'avalanche',
   aviatrices: 'aviatrix',
   avionics: 'avionics',
+  avoirdupois: 'avoirdupois',
+  avoirdupoises: 'avoirdupois',
   axes: 'axis',
-  bacillis: 'bacilli',
+  bacillus: 'bacillus',
   backaches: 'backache',
   backhoes: 'backhoe',
   backstairs: 'backstairs',
   backwoods: 'backwoods',
   badlands: 'badlands',
-  bandittis: 'banditti',
-  banis: 'bani',
   banns: 'banns',
   bassis: 'bassi',
   bathos: 'bathos',
   bayous: 'bayou',
-  beaus: 'beau',
   bedclothes: 'bedclothes',
   beeves: 'beef',
   behalves: 'behalf',
   belies: 'belie',
   bellyaches: 'bellyache',
   bemuses: 'bemuse',
-  beriberis: 'beriberi',
   bias: 'bias',
   biases: 'bias',
   biceps: 'biceps',
   bicepses: 'biceps',
   biggies: 'biggie',
-  bikinis: 'bikini',
   billiards: 'billiards',
   biophysics: 'biophysics',
   birdies: 'birdie',
   blice: 'blouse',
   blintzes: 'blintze',
+  bogus: 'bogus',
   bonkers: 'bonkers',
   bonnies: 'bonnie',
-  bonsais: 'bonsai',
   boogies: 'boogie',
   bookies: 'bookie',
   bookshelves: 'bookshelf',
   boondocks: 'boondocks',
   bouillabaisses: 'bouillabaisse',
+  bourgeois: 'bourgeois',
+  bourgeoises: 'bourgeois',
   bourgeoisies: 'bourgeoisie',
   breakpoints: 'breakpoints',
   britches: 'britches',
-  broccolis: 'broccoli',
-  bronchis: 'bronchi',
-  brontosauris: 'brontosauri',
+  bronchitis: 'bronchitis',
+  bronchitises: 'bronchitis',
+  bronchus: 'bronchus',
+  brontosaurus: 'brontosaurus',
   brownies: 'brownie',
   budgies: 'budgie',
-  bureaus: 'bureau',
   burnouses: 'burnous',
+  bursitis: 'bursitis',
+  bursitises: 'bursitis',
   butterfingers: 'butterfingers',
   caches: 'cache',
-  cactis: 'cacti',
-  caduceis: 'caducei',
-  calculis: 'calculi',
+  cactus: 'cactus',
+  caduceus: 'caduceus',
+  calculus: 'calculus',
   callisthenics: 'callisthenics',
   callouses: 'callous',
+  callus: 'callus',
   calories: 'calorie',
   calves: 'calf',
   calyces: 'calyces',
   camaraderies: 'camaraderie',
-  campanilis: 'campanili',
+  cannabis: 'cannabis',
   cannabises: 'cannabis',
   canoes: 'canoe',
   carbs: 'carbs',
   caribous: 'caribou',
   caries: 'caries',
-  carpis: 'carpi',
+  carpus: 'carpus',
   caryatides: 'caryatid',
   catharses: 'catharsis',
-  cellis: 'celli',
+  caucus: 'caucus',
+  census: 'census',
   cervices: 'cervix',
-  chichis: 'chichi',
+  chamois: 'chamois',
+  chamoises: 'chamois',
+  chateaus: 'chateaus',
   chilies: 'chili',
-  chilis: 'chili',
-  chillis: 'chilli',
-  chis: 'chi',
   chitlings: 'chitlings',
   chitlins: 'chitlins',
   chitterlings: 'chitterlings',
+  chorus: 'chorus',
   chrysalides: 'chrysalides',
+  chrysalis: 'chrysalis',
   chrysalises: 'chrysalis',
+  circus: 'circus',
+  cirrus: 'cirrus',
+  cis: 'cis',
+  cises: 'cis',
+  citrus: 'citrus',
   civies: 'civies',
   civvies: 'civvies',
+  clematis: 'clematis',
   clematises: 'clematis',
-  cliis: 'clii',
+  clitoris: 'clitoris',
   clitorises: 'clitoris',
   cloches: 'cloche',
   cloverleaves: 'cloverleaf',
-  clviis: 'clvii',
-  clvis: 'clvi',
-  clxiis: 'clxii',
-  clxis: 'clxi',
-  clxviis: 'clxvii',
-  clxvis: 'clxvi',
-  coccis: 'cocci',
+  coccus: 'coccus',
   coccyges: 'coccyges',
   cockamamies: 'cockamamie',
   codices: 'codex',
+  coitus: 'coitus',
+  colitis: 'colitis',
+  colitises: 'colitis',
   collies: 'collie',
   colones: 'colon',
   colossis: 'colossi',
-  concertis: 'concerti',
-  confettis: 'confetti',
+  colossus: 'colossus',
   confuses: 'confuse',
+  conjunctivitis: 'conjunctivitis',
+  conjunctivitises: 'conjunctivitis',
   conquistadores: 'conquistador',
   cons: 'cons',
+  consensus: 'consensus',
   conses: 'cons',
   contretemps: 'contretemps',
   contuses: 'contuse',
@@ -177,101 +194,111 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   coolies: 'coolie',
   cooties: 'cootie',
   cornflakes: 'cornflakes',
+  corpus: 'corpus',
   cortices: 'cortex',
   cosmos: 'cosmos',
   cosmoses: 'cosmos',
   coteries: 'coterie',
-  crescendis: 'crescendi',
   crevasses: 'crevasse',
-  crocis: 'croci',
+  crocus: 'crocus',
   crofts: 'crofts',
   crossbones: 'crossbones',
   crossways: 'crossways',
   cryogenics: 'cryogenics',
-  cumulis: 'cumuli',
+  cumulus: 'cumulus',
+  cunnilingus: 'cunnilingus',
   curies: 'curie',
-  daiquiris: 'daiquiri',
+  dais: 'dais',
   daises: 'dais',
-  dashikis: 'dashiki',
   dds: 'dds',
   deaves: 'deaf',
   debases: 'debase',
+  debris: 'debris',
+  debrises: 'debris',
   decrements: 'decrements',
-  decrescendis: 'decrescendi',
   defuses: 'defuse',
-  delis: 'deli',
   deluxes: 'deluxe',
   demitasses: 'demitasse',
+  dermatitis: 'dermatitis',
+  dermatitises: 'dermatitis',
+  dermis: 'dermis',
+  dermises: 'dermis',
   detentes: 'detentes',
-  dhotis: 'dhoti',
+  detritus: 'detritus',
   diabetes: 'diabetes',
   dialyzes: 'dialyzes',
   diereses: 'dieresis',
   dies: 'die',
   diffuses: 'diffuse',
-  dilettantis: 'dilettanti',
+  digitalis: 'digitalis',
+  digitalises: 'digitalis',
+  dis: 'dis',
   disabuses: 'disabuse',
+  discus: 'discus',
+  dises: 'dis',
   disuses: 'disuse',
-  djinnis: 'djinni',
   does: 'doe',
   dogies: 'dogie',
   doldrums: 'doldrums',
   dos: 'dos',
   douches: 'douche',
   downstairs: 'downstairs',
-  dpis: 'dpi',
-  drachmais: 'drachmai',
   dreadlocks: 'dreadlocks',
   dregs: 'dregs',
   drouthes: 'drouth',
   dwarves: 'dwarf',
   earaches: 'earache',
-  ecrus: 'ecru',
   edgeways: 'edgeways',
   eds: 'eds',
   eeries: 'eerie',
+  egis: 'egis',
+  egises: 'egis',
   electrodynamics: 'electrodynamics',
   ellipses: 'ellipsis',
   elves: 'elf',
-  emojis: 'emoji',
+  emeritus: 'emeritus',
   emphases: 'emphasis',
   ems: 'ems',
-  emus: 'emu',
+  encephalitis: 'encephalitis',
+  encephalitises: 'encephalitis',
   endways: 'endways',
-  ennuis: 'ennui',
   enthuses: 'enthuse',
   entrails: 'entrails',
   environs: 'environs',
+  epidermis: 'epidermis',
   epidermises: 'epidermis',
   epiglottides: 'epiglottides',
+  epiglottis: 'epiglottis',
   epiglottises: 'epiglottis',
-  esophagis: 'esophagi',
+  esophagus: 'esophagus',
   ethos: 'ethos',
-  eucalyptis: 'eucalypti',
+  eucalyptus: 'eucalyptus',
   eugenics: 'eugenics',
   excuses: 'excuse',
   executrices: 'executrix',
   exegeses: 'exegesis',
   exes: 'exes',
+  exodus: 'exodus',
   faeces: 'faeces',
   fairings: 'fairings',
   feces: 'feces',
+  fetus: 'fetus',
   fezes: 'fez',
   fezzes: 'fezzes',
   fiches: 'fiche',
   fiddlesticks: 'fiddlesticks',
   fies: 'fie',
   finesses: 'finesse',
+  finis: 'finis',
   finises: 'finis',
   fishwives: 'fishwife',
   fisticuffs: 'fisticuffs',
   flambes: 'flambes',
   floes: 'floe',
   flyleaves: 'flyleaf',
-  focis: 'foci',
   focusses: 'focusses',
   foes: 'foe',
-  fondus: 'fondu',
+  foetus: 'foetus',
   footlights: 'footlights',
   footsies: 'footsie',
   forceps: 'forceps',
@@ -281,33 +308,35 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   freebases: 'freebase',
   freebies: 'freebie',
   ftpers: 'ftpers',
-  fungis: 'fungi',
+  fungus: 'fungus',
   fuses: 'fuse',
   gallowses: 'gallows',
   gas: 'gas',
   gases: 'gas',
   gasses: 'gasses',
+  gastritis: 'gastritis',
+  gastritises: 'gastritis',
   gasworks: 'gasworks',
   gauches: 'gauche',
   geneses: 'genesis',
   genies: 'genie',
-  geniis: 'genii',
+  genius: 'genius',
   geniuses: 'genius',
   geocaches: 'geocache',
   geophysics: 'geophysics',
   geopolitics: 'geopolitics',
-  gladiolis: 'gladioli',
-  glissandis: 'glissandi',
+  gingivitis: 'gingivitis',
+  gingivitises: 'gingivitis',
+  gladiolus: 'gladiolus',
   glottides: 'glottides',
+  glottis: 'glottis',
   glottises: 'glottis',
-  gnus: 'gnu',
   goalies: 'goalie',
   goes: 'goes',
-  graffitis: 'graffiti',
+  gratis: 'gratis',
+  gratises: 'gratis',
   groupies: 'groupie',
-  gurus: 'guru',
   haemorrhoids: 'haemorrhoids',
-  haikus: 'haiku',
   halves: 'half',
   handkerchieves: 'handkerchief',
   has: 'has',
@@ -316,296 +345,289 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   heartaches: 'heartache',
   heartstrings: 'heartstrings',
   helices: 'helix',
+  hepatitis: 'hepatitis',
+  hepatitises: 'hepatitis',
   herpes: 'herpes',
   herselves: 'herself',
-  hibachis: 'hibachi',
+  hiatus: 'hiatus',
+  hibiscus: 'hibiscus',
   hies: 'hie',
   himselves: 'himself',
-  hippopotamis: 'hippopotami',
+  hippopotamus: 'hippopotamus',
+  his: 'his',
+  hises: 'his',
   hoes: 'hoe',
   hoodies: 'hoodie',
   hooves: 'hoof',
   horseshoes: 'horseshoe',
   hos: 'hos',
+  houmus: 'houmus',
   housewares: 'housewares',
   housewives: 'housewife',
   hrs: 'hrs',
-  humeris: 'humeri',
+  hubris: 'hubris',
+  hubrises: 'hubris',
+  humerus: 'humerus',
+  hummus: 'hummus',
+  humus: 'humus',
   hustings: 'hustings',
   hypnoses: 'hypnosis',
   hypotenuses: 'hypotenuse',
-  hypothalamis: 'hypothalami',
+  hypothalamus: 'hypothalamus',
   ibices: 'ibex',
+  ibis: 'ibis',
   ibises: 'ibis',
   ides: 'ides',
   ids: 'ids',
   ifs: 'ifs',
-  iiis: 'iii',
+  ignoramus: 'ignoramus',
+  illus: 'illus',
   impasses: 'impasse',
-  impromptus: 'impromptu',
-  incubis: 'incubi',
+  impetus: 'impetus',
   infuses: 'infuse',
   innards: 'innards',
   ins: 'ins',
-  intaglis: 'intagli',
-  intermezzis: 'intermezzi',
   intravenouses: 'intravenous',
+  iris: 'iris',
   irises: 'iris',
   isosceles: 'isosceles',
-  isthmis: 'isthmi',
+  isthmus: 'isthmus',
   its: 'its',
   itselves: 'itself',
   jackknives: 'jackknife',
   jaggies: 'jaggies',
   jalousies: 'jalousie',
   jeans: 'jeans',
-  jinnis: 'jinni',
   jitters: 'jitters',
-  jiujitsus: 'jiujitsu',
   jodhpurs: 'jodhpurs',
-  jujitsus: 'jujitsu',
-  jujutsus: 'jujutsu',
   kerchieves: 'kerchief',
-  khakis: 'khaki',
-  kiwis: 'kiwi',
   knickers: 'knickers',
   knives: 'knife',
   kohlrabies: 'kohlrabi',
-  kohlrabis: 'kohlrabi',
   kookies: 'kookie',
   kudos: 'kudos',
-  kudzus: 'kudzu',
   lacrosses: 'lacrosse',
   laddies: 'laddie',
   largesses: 'largesse',
   larynges: 'larynges',
+  laryngitis: 'laryngitis',
+  laryngitises: 'laryngitis',
   lassies: 'lassie',
   lazybones: 'lazybones',
   lbs: 'lbs',
   leaves: 'leaf',
   leftwards: 'leftwards',
-  leis: 'lei',
   lengthways: 'lengthways',
   lens: 'lens',
   lenses: 'lens',
   levellers: 'levellers',
-  librettis: 'libretti',
   lies: 'lie',
-  lieus: 'lieu',
   lifeforms: 'lifeforms',
-  liis: 'lii',
   lingeries: 'lingerie',
-  litchis: 'litchi',
-  literatis: 'literati',
+  litmus: 'litmus',
   lives: 'life',
   loaves: 'loaf',
-  locis: 'loci',
+  locus: 'locus',
   looneyies: 'looneyies',
-  luaus: 'luau',
-  lviis: 'lvii',
-  lvis: 'lvi',
-  lxiis: 'lxii',
-  lxis: 'lxi',
-  lxviis: 'lxvii',
-  lxvis: 'lxvi',
+  lotus: 'lotus',
+  lupus: 'lupus',
   macaronies: 'macaroni',
-  macaronis: 'macaroni',
   madras: 'madras',
   madrases: 'madras',
-  maestris: 'maestri',
   magpies: 'magpie',
-  maharanis: 'maharani',
-  maharishis: 'maharishi',
   mantes: 'mantis',
+  mantis: 'mantis',
   mantises: 'mantis',
   marabous: 'marabou',
-  mariachis: 'mariachi',
-  martinis: 'martini',
+  marquis: 'marquis',
+  marquises: 'marquis',
   mas: 'mas',
   matins: 'matins',
   meatloaves: 'meatloaf',
+  megalopolis: 'megalopolis',
   megalopolises: 'megalopolis',
   menageries: 'menagerie',
+  meningitis: 'meningitis',
+  meningitises: 'meningitis',
   menservants: 'menservants',
   menses: 'menses',
-  menus: 'menu',
   mes: 'mes',
   mesdames: 'mesdames',
   mesdemoiselles: 'mesdemoiselles',
   messieurs: 'messieurs',
-  metacarpis: 'metacarpi',
+  metacarpus: 'metacarpus',
   metaphysics: 'metaphysics',
   metastases: 'metastasis',
   methinks: 'methinks',
+  metropolis: 'metropolis',
   metropolises: 'metropolis',
   microeconomics: 'microeconomics',
   microfiches: 'microfiche',
   microfloppies: 'microfloppies',
   microplastics: 'microplastics',
   midwives: 'midwife',
-  milieus: 'milieu',
   minibusses: 'minibusses',
   minifloppies: 'minifloppies',
-  minis: 'mini',
   miniseries: 'miniseries',
   mistletoes: 'mistletoe',
   misuses: 'misuse',
+  modulus: 'modulus',
   molasses: 'molasses',
   monies: 'monies',
-  monsignoris: 'monsignori',
   mos: 'mos',
   mousses: 'mousse',
   moustaches: 'moustache',
-  mueslis: 'muesli',
-  muftis: 'mufti',
-  multis: 'multi',
+  mucus: 'mucus',
   munchies: 'munchies',
   muses: 'muse',
   mustaches: 'mustache',
-  muumuus: 'muumuu',
   mynahes: 'mynah',
   myselves: 'myself',
   naiades: 'naiad',
   narcissis: 'narcissi',
-  nautilis: 'nautili',
+  narcissus: 'narcissus',
+  nautilus: 'nautilus',
   neckerchieves: 'neckerchief',
   neckties: 'necktie',
   nemeses: 'nemesis',
+  nephritis: 'nephritis',
+  nephritises: 'nephritis',
+  neuritis: 'neuritis',
+  neuritises: 'neuritis',
   neuroses: 'neurosis',
   newbies: 'newbie',
   newsagents: 'newsagents',
+  nexus: 'nexus',
   niches: 'niche',
   nightclothes: 'nightclothes',
   nightlives: 'nightlife',
-  nimbis: 'nimbi',
   noes: 'noes',
+  nonplus: 'nonplus',
   nonplusses: 'nonplusses',
   nos: 'nos',
   nowadays: 'nowadays',
-  nucleis: 'nuclei',
+  nucleus: 'nucleus',
   nucleuses: 'nucleus',
   oases: 'oasis',
   oboes: 'oboe',
   obtuses: 'obtuse',
-  octopis: 'octopi',
   oftentimes: 'oftentimes',
   ohs: 'ohs',
   oldies: 'oldie',
   omnibusses: 'omnibusses',
   oneselves: 'oneself',
+  onus: 'onus',
   oodles: 'oodles',
   oops: 'oops',
   ops: 'ops',
+  opus: 'opus',
   organdies: 'organdie',
-  origamis: 'origami',
-  ormolus: 'ormolu',
   ourselves: 'ourselves',
   overseas: 'overseas',
   overshoes: 'overshoe',
   overuses: 'overuse',
   pajamas: 'pajamas',
-  palazzis: 'palazzi',
   pampas: 'pampas',
   panaches: 'panache',
   pancreas: 'pancreas',
   pancreases: 'pancreas',
   pantaloons: 'pantaloons',
-  papyris: 'papyri',
+  papyrus: 'papyrus',
   paratroops: 'paratroops',
-  parvenus: 'parvenu',
   pas: 'pas',
   pastiches: 'pastiche',
-  pastramis: 'pastrami',
   pathos: 'pathos',
+  patois: 'patois',
+  patoises: 'patois',
   pecs: 'pecs',
   pekoes: 'pekoe',
   pelves: 'pelvis',
+  pelvis: 'pelvis',
   pelvises: 'pelvis',
   penes: 'penis',
+  penis: 'penis',
   penises: 'penis',
   penknives: 'penknife',
-  pepperonis: 'pepperoni',
   perhaps: 'perhaps',
   periphrases: 'periphrasis',
+  peritonitis: 'peritonitis',
+  peritonitises: 'peritonitis',
   peruses: 'peruse',
   phalanges: 'phalanges',
-  phallis: 'phalli',
+  phallus: 'phallus',
   pharynges: 'pharynges',
-  pianissimis: 'pianissimi',
+  phlebitis: 'phlebitis',
+  phlebitises: 'phlebitis',
+  phosphorus: 'phosphorus',
   piazzes: 'piazze',
-  piccalillis: 'piccalilli',
   pies: 'pie',
-  pilaus: 'pilau',
-  pizzicatis: 'pizzicati',
+  pis: 'pis',
+  pises: 'pis',
   plainclothes: 'plainclothes',
-  plateaus: 'plateau',
-  platypis: 'platypi',
+  platypus: 'platypus',
+  plexus: 'plexus',
   pliers: 'pliers',
+  plus: 'plus',
   plusses: 'plusses',
   pocketknives: 'pocketknife',
-  pois: 'poi',
+  poliomyelitis: 'poliomyelitis',
+  poliomyelitises: 'poliomyelitis',
   politesses: 'politesse',
+  portcullis: 'portcullis',
   portcullises: 'portcullis',
-  portmanteaus: 'portmanteau',
   potpies: 'potpie',
-  potpourris: 'potpourri',
   prairies: 'prairie',
   pres: 'pres',
   proboscides: 'proboscides',
+  proboscis: 'proboscis',
   proboscises: 'proboscis',
   profuses: 'profuse',
+  prospectus: 'prospectus',
   psychoses: 'psychosis',
+  pus: 'pus',
   quadriceps: 'quadriceps',
   quadricepses: 'quadriceps',
   quasis: 'quasi',
   ques: 'ques',
   quiches: 'quiche',
   quickies: 'quickie',
+  quietus: 'quietus',
   quizzes: 'quizzes',
-  rabbis: 'rabbi',
   rabies: 'rabies',
-  radiis: 'radii',
+  radius: 'radius',
   radiuses: 'radius',
-  raviolis: 'ravioli',
   reales: 'real',
   recluses: 'recluse',
+  refocus: 'refocus',
   refocusses: 'refocusses',
   refuses: 'refuse',
-  rehis: 'rehi',
+  reis: 'reis',
+  reises: 'reis',
   rendezvouses: 'rendezvous',
-  rhinoceris: 'rhinoceri',
   rhinoceros: 'rhinoceros',
   rhinoceroses: 'rhinoceros',
-  rhombis: 'rhombi',
   rickets: 'rickets',
   roes: 'roe',
   rookies: 'rookie',
   rotisseries: 'rotisserie',
   rps: 'rps',
+  ruckus: 'ruckus',
+  rumpus: 'rumpus',
   ruses: 'ruse',
   sades: 'sad',
-  safaris: 'safari',
-  sakis: 'saki',
-  salamis: 'salami',
-  samurais: 'samurai',
   sans: 'sans',
-  sarcophagis: 'sarcophagi',
-  saris: 'sari',
+  sarcophagus: 'sarcophagus',
   sassafras: 'sassafras',
   sassafrases: 'sassafras',
   savannahes: 'savannah',
   scabies: 'scabies',
   scampies: 'scampi',
-  scampis: 'scampi',
   scarves: 'scarf',
-  scherzis: 'scherzi',
   schnapps: 'schnapps',
   schooldays: 'schooldays',
   selfies: 'selfie',
   selves: 'self',
   semiotics: 'semiotics',
-  semis: 'semi',
-  shanghais: 'shanghai',
   sheaves: 'sheaf',
   shelves: 'shelf',
   shoes: 'shoe',
@@ -613,38 +635,33 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   shuckses: 'shucks',
   sideburns: 'sideburns',
   sideways: 'sideways',
-  situs: 'situ',
-  skis: 'ski',
+  sinus: 'sinus',
+  sinusitis: 'sinusitis',
+  sinusitises: 'sinusitis',
   sloes: 'sloe',
   smithereens: 'smithereens',
   smoothes: 'smooth',
-  snafus: 'snafu',
   snowshoes: 'snowshoe',
   soapsuds: 'soapsuds',
-  solis: 'soli',
   sorties: 'sortie',
   sos: 'sos',
   spareribs: 'spareribs',
   sphinges: 'sphinges',
-  spumonis: 'spumoni',
-  staccatis: 'staccati',
-  staphylococcis: 'staphylococci',
-  stimulis: 'stimuli',
+  staphylococcus: 'staphylococcus',
+  stimulus: 'stimulus',
   stomachaches: 'stomachache',
-  streptococcis: 'streptococci',
-  stylis: 'styli',
+  streptococcus: 'streptococcus',
+  stylus: 'stylus',
   stymies: 'stymie',
   suds: 'suds',
   suffuses: 'suffuse',
-  sukiyakis: 'sukiyaki',
   sunglasses: 'sunglasses',
-  sushis: 'sushi',
-  swamis: 'swami',
+  surplus: 'surplus',
   sweatpants: 'sweatpants',
   sweeties: 'sweetie',
-  syllabis: 'syllabi',
   symbioses: 'symbiosis',
-  tableaus: 'tableau',
+  syphilis: 'syphilis',
+  syphilises: 'syphilis',
   tabus: 'tabu',
   takeaways: 'takeaways',
   taxies: 'taxi',
@@ -654,34 +671,41 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   teargases: 'teargas',
   teargasses: 'teargasses',
   tectonics: 'tectonics',
-  tempis: 'tempi',
-  terminis: 'termini',
-  thalamis: 'thalami',
+  tendinitis: 'tendinitis',
+  tendinitises: 'tendinitis',
+  tendonitis: 'tendonitis',
+  tendonitises: 'tendonitis',
+  terminus: 'terminus',
+  tetanus: 'tetanus',
+  thalamus: 'thalamus',
   themselves: 'themselves',
   thermos: 'thermos',
   thermoses: 'thermos',
-  thesauris: 'thesauri',
+  thesaurus: 'thesaurus',
   thieves: 'thief',
+  this: 'this',
+  thises: 'this',
   thoraces: 'thoraces',
   thous: 'thou',
   throes: 'throe',
   thromboses: 'thrombosis',
-  thrus: 'thru',
-  thymis: 'thymi',
+  thus: 'thus',
+  thymus: 'thymus',
   thyselves: 'thyself',
   tiddlywinks: 'tiddlywinks',
   ties: 'tie',
-  timpanis: 'timpani',
-  tipis: 'tipi',
   tiptoes: 'tiptoe',
   toes: 'toe',
-  tofus: 'tofu',
+  tonsillitis: 'tonsillitis',
+  tonsillitises: 'tonsillitis',
   toothaches: 'toothache',
   topazes: 'topaz',
   torsis: 'torsi',
+  torus: 'torus',
   trans: 'trans',
   transfuses: 'transfuse',
   treas: 'treas',
+  trellis: 'trellis',
   trellises: 'trellis',
   triceps: 'triceps',
   tricepses: 'triceps',
@@ -689,13 +713,12 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   triceratopses: 'triceratops',
   trifocals: 'trifocals',
   tripos: 'tripos',
-  trousseaus: 'trousseau',
-  tsunamis: 'tsunami',
   ttys: 'ttys',
   turves: 'turf',
-  tutus: 'tutu',
   tweezers: 'tweezers',
-  umbilicis: 'umbilici',
+  typhus: 'typhus',
+  tyrannosaurus: 'tyrannosaurus',
+  umbilicus: 'umbilicus',
   underclothes: 'underclothes',
   underlies: 'underlie',
   underpants: 'underpants',
@@ -704,17 +727,16 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   unties: 'untie',
   ups: 'ups',
   upstairs: 'upstairs',
-  uteris: 'uteri',
+  uterus: 'uterus',
   veggies: 'veggie',
+  verdigris: 'verdigris',
   verdigrises: 'verdigris',
-  vermicellis: 'vermicelli',
+  versus: 'versus',
   vies: 'vie',
-  viiis: 'viii',
-  viis: 'vii',
   virtuosis: 'virtuosi',
+  viscus: 'viscus',
   vortices: 'vortex',
-  wadis: 'wadi',
-  wapitis: 'wapiti',
+  walrus: 'walrus',
   was: 'was',
   waterworks: 'waterworks',
   wedgies: 'wedgie',
@@ -723,7 +745,6 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   wharves: 'wharf',
   wheelbases: 'wheelbase',
   whereabouts: 'whereabouts',
-  wikis: 'wiki',
   wildlives: 'wildlife',
   willies: 'willies',
   wives: 'wife',
@@ -731,36 +752,11 @@ export const SINGULAR_EXCEPTIONS: Record<string, string> = {
   wizzes: 'wizzes',
   woes: 'woe',
   wolves: 'wolf',
-  xciis: 'xcii',
-  xcis: 'xci',
-  xcviis: 'xcvii',
-  xcvis: 'xcvi',
-  xiiis: 'xiii',
-  xiis: 'xii',
-  xviiis: 'xviii',
-  xviis: 'xvii',
-  xvis: 'xvi',
-  xxiiis: 'xxiii',
-  xxiis: 'xxii',
-  xxis: 'xxi',
-  xxviiis: 'xxviii',
-  xxviis: 'xxvii',
-  xxvis: 'xxvi',
-  xxxiiis: 'xxxiii',
-  xxxiis: 'xxxii',
-  xxxis: 'xxxi',
-  xxxviiis: 'xxxviii',
-  xxxviis: 'xxxvii',
-  xxxvis: 'xxxvi',
   yes: 'yes',
   yeses: 'yes',
-  yetis: 'yeti',
-  yogis: 'yogi',
   yourselves: 'yourself',
   yous: 'you',
   yrs: 'yrs',
   zebus: 'zebu',
   zombies: 'zombie',
-  zombis: 'zombi',
-  zucchinis: 'zucchini',
 };
diff --git a/packages/inflekt/src/rules.ts b/packages/inflekt/src/rules.ts
index 9a3f39c..0004e83 100644
--- a/packages/inflekt/src/rules.ts
+++ b/packages/inflekt/src/rules.ts
@@ -78,11 +78,18 @@ export const F_STEM_PLURALS: Array<[string, string]> = [
 ];
 
 /**
- * Words that are already singular but look plural to the s$ rule: no English
- * plural ends in "is" (iris, analysis, chassis) or "us" (bus, status, virus,
- * anxious).
+ * Adjectives, never plurals: anxious, various, porous. No noun stem ends in
+ * "ou", so nothing here is ever a dropped-s away from a singular.
+ *
+ * There is no equivalent rule for the rest of "-is"/"-us", because none exists:
+ * "apis" and "iris" are both a vowel plus "s" (api + s, iri + s), so no suffix
+ * tells the plural from the singular. Whether a word is one or the other is a
+ * dictionary fact, and the dictionary-proven singulars live in
+ * SINGULAR_EXCEPTIONS as self-mappings (status -> status, analysis -> analysis).
+ * Words the dictionary does not know fall through to the generic "drop the s",
+ * which is what coined identifiers want: apis -> api, cpus -> cpu, uris -> uri.
  */
-const ALREADY_SINGULAR_REGEX = /(?:is|us)$/i;
+const ADJECTIVE_OUS_REGEX = /ous$/i;
 
 /**
  * The only -ice plurals. The inflection library's rule is written `([m|l])ice`,
@@ -212,7 +219,7 @@ export function singularizeByRules(word: string): string {
   const normalizedWord = normalizeMalformedDoubleS(word);
   const lowerWord = normalizedWord.toLowerCase();
 
-  if (ALREADY_SINGULAR_REGEX.test(normalizedWord)) {
+  if (ADJECTIVE_OUS_REGEX.test(normalizedWord)) {
     return normalizedWord;
   }