Irregular plurals, explained

Most English nouns just take -s. These are the ones people actually look up, with the pattern behind each exception.

The full list (152 nouns)

afterlife: afterlives
aircraft: aircraft
alias: aliases
analysis: analyses
anime: anime
apex: apices
appendix: appendices
aqua: aquae
arthritis: arthritides
atlas: atlases
avocado: avocados
axis: axes
banjo: banjos
basis: bases
batman: batmen
behalf: behalves
belief: beliefs
bison: bison
bonus: bonuses
buffalo: buffaloes
bus: buses
calculus: calculi
calf: calves
campus: campuses
canvas: canvases
cargo: cargoes
chairman: chairmen
charisma: charismata
chef: chefs
chief: chiefs
child: children
chili: chiles
cholera: cholerae
circus: circuses
cliff: cliffs
cod: cod
colon: cola
corps: corps
corpus: corpora
cortex: cortices
craft: craft
criterion: criteria
curriculum: curricula
deer: deer
diagnosis: diagnoses
dialysis: dialyses
dice: dice
diva: dive
dwarf: dwarfs
echo: echoes
elf: elves
embargo: embargoes
emphasis: emphases
equilibrium: equilibria
fish: fish
flamingo: flamingos
foot: feet
foreman: foremen
freeman: freemen
freshman: freshmen
gas: gases
genius: geniuses
gentleman: gentlemen
goodman: goodmen
goose: geese
half: halves
halo: halos
headquarters: headquarters
hepatitis: hepatitides
hero: heroes
hoof: hooves
housewife: house-wives
hypothesis: hypotheses
index: indices
iris: irises
kangaroo: kangaroos
knife: knives
leaf: leaves
lens: lenses
lied: lieder
life: lives
loaf: loaves
man: men
mango: mangoes
matrix: matrices
maximum: maxima
means: means
medium: media
millennium: millennia
money: monies
monsieur: messieurs
moose: moose
mosquito: mosquitoes
motto: mottos
mouse: mice
nemesis: nemeses
ninja: ninja
nucleus: nuclei
oasis: oases
octopus: octopuses
offspring: offspring
optimum: optima
paralysis: paralyses
penny: pence
percent: percent
photo: photos
piano: pianos
policeman: policemen
potato: potatoes
prognosis: prognoses
quiz: quizzes
radius: radii
roof: roofs
salmon: salmon
scarf: scarves
sclerosis: scleroses
self: selves
sent: senti
series: series
sheep: sheep
shelf: shelves
shrimp: shrimp
spacecraft: spacecraft
species: species
spectrum: spectra
standby: stand-bys
stella: stellae
stimulus: stimuli
superman: supermen
swine: swine
syllabus: syllabi
synopsis: synopses
synthesis: syntheses
thief: thieves
tomato: tomatoes
tooth: teeth
tornado: tornadoes
torpedo: torpedoes
trout: trout
tuxedo: tuxedos
uterus: uteri
veto: vetoes
virus: viruses
volcano: volcanoes
vortex: vortices
walrus: walruses
werewolf: werewolves
wharf: wharves
wife: wives
wolf: wolves
woman: women
zero: zeros

The five patterns behind the chaos

Old English survivors: vowel changes (man, men; foot, feet) and the ancient -en ending (child, children; ox, oxen).
F to V: knife, knives; leaf, leaves; wolf, wolves. Not universal: roofs and chiefs stay regular, which is why people check.
Classical borrowings: Latin and Greek endings kept their home-language plurals: analysis, analyses; criterion, criteria; cactus, cacti.
Invariants: sheep, deer, species, aircraft. Same word both ways; context does the work.
False classics: octopus looks Latin but is Greek, so the pedantic "octopi" is wrong on its own terms. Octopuses is standard.

Each linked page shows the plural, the reason, and real example sentences, plus the word's synonyms and rhymes if you are there to write rather than to settle a bet.