Plurals
Most English nouns just add -s. The ones on this hub don't, and each has a real, traceable reason — borrowed Latin and Greek endings, sound changes from Old English, or nouns that simply never took a plural marker at all. This hub groups the patterns so the exceptions stop looking random and starts looking like three or four genuinely separate historical layers.
The Latin and Greek layer
A large cluster of irregular plurals — cactus/cacti, criterion/criteria, analysis/analyses, formula/formulae, appendix/appendices — comes from words borrowed wholesale from Latin or Greek, often through academic, scientific, or legal usage, along with their original plural endings still attached. English speakers kept the foreign plural pattern (-us to -i, -on to -a, -is to -es, -a to -ae, -ix to -ices) for as long as the word stayed associated with formal or technical registers; several of these are now drifting toward regular -s plurals in everyday speech (cactuses, formulas, indexes) precisely because the words have become common enough that the -s rule takes over, mirroring the same frequency effect that governs irregular verbs. Octopus is the clearest example of how messy this gets: it's actually Greek in origin, not Latin, so the "correct" classical plural would be octopodes, not the Latin-style octopi that many people use anyway — and both are now rarer in practice than the fully anglicized octopuses.
The Old English mutation layer
A second, older cluster — foot/feet, tooth/teeth, mouse/mice, goose/geese, man/men, woman/women, louse/lice — traces to a completely different mechanism than the Latin/Greek borrowings above: a lost Old English plural suffix once tugged the root vowel of the word toward the front of the mouth, and once that suffix itself eroded away and disappeared from pronunciation, only its side-effect on the vowel survived as the plural marker. Linguists call this process i-mutation, and because it's a purely native Germanic sound change with no borrowing involved, it only ever touched a small, closed set of old, everyday nouns rather than spreading to new vocabulary. Child/children is a rarer double-marked plural, keeping an old -er plural (as in German Kinder) and then adding -en on top of it, likely reinforced by analogy with other -en plurals like oxen and brethren once those became rare enough to feel irregular rather than standard.
Zero plurals and collective nouns
A third group — sheep, deer, fish, moose, species, aircraft, salmon, trout — takes no plural marker whatsoever, the singular and plural forms being flatly identical. Nearly all of them name animals people traditionally hunted, herded, or fished in bulk, and Old English grammar happened to assign them to a noun class where singular and plural already looked alike well before any of the sound changes described above ever took hold; a hunter rarely needs a sentence to distinguish "one deer" from "many deer" when the surrounding context already makes the count obvious. "Fish" can also take a regular plural (fishes) specifically when referring to multiple species rather than multiple individual fish — "the fishes of the Amazon" versus "I caught three fish" — which is one of the few irregular-plural distinctions that carries real semantic meaning rather than just being a fossil of an older sound system.
The -f/-fe to -ves pattern
A fourth cluster — leaf/leaves, knife/knives, wife/wives, wolf/wolves, half/halves, shelf/shelves, calf/calves, thief/thieves, loaf/loaves, life/lives — comes down to plain phonetics: Old English speech turned an /f/ sound into a /v/ sound whenever it landed between two vowels, and that's precisely the position a final /f/ found itself in once the old plural ending (a full syllable, not just a bare -s) was tacked on after it. Centuries later, that extra vowel wore away from pronunciation entirely, but the voicing effect it had triggered stuck around, fossilized into the modern spelling even though nothing in the current pronunciation still explains it. Not every -f noun follows this pattern — roof, chief, belief, and cliff simply add -s (roofs, chiefs, beliefs, cliffs) — because usage has been drifting away from the voicing pattern for centuries, and dictionaries increasingly list both "hoofs" and "hooves," "scarfs" and "scarves" as acceptable, another live in-progress regularization exactly parallel to what's happening with dreamed/dreamt in the verb system.
The -o to -oes question
Nouns ending in -o split unpredictably between adding -s and adding -es: potatoes and tomatoes take -es, but pianos and photos take -s, with no fully reliable rule to predict which. The rough historical pattern is that older, more thoroughly assimilated -o words (hero, potato, echo, veto, coming through French or directly from Old English contexts) took -es, while more recent borrowings — especially musical and technical terms often taken directly from Italian in the 18th-19th centuries (piano, solo, tempo, studio) — kept the simpler -s. Dictionaries disagree on several borderline cases (mosquitoes/mosquitos, volcanoes/volcanos are both attested), which is one of the few places in the plural system where you genuinely have to check a specific word rather than apply a rule.
Foreign plurals beyond Latin and Greek
The Latin and Greek borrowings covered above aren't the only foreign plural patterns living inside English. French loanwords sometimes keep their French plural spelling even where the pronunciation has anglicized: bureau/bureaux and chateau/chateaux both admit the plain -s alternative (bureaus, chateaus) in everyday American usage, but the -x form still shows up regularly in edited writing, especially in British English. Italian gave English a cluster of -o words that keep their Italian -i plural rather than taking English -s or -es: paparazzo/paparazzi, graffito/graffiti, virtuoso/virtuosi (alongside the equally accepted virtuosos). A smaller, more striking group comes from Hebrew by way of Biblical translation: cherub/cherubim and seraph/seraphim keep the Hebrew -im plural ending in religious and literary contexts, though "cherubs" is now standard in ordinary speech referring to chubby-faced children or decorative figures rather than the angelic order.
Plural-only nouns and singular-looking plurals
A distinct category has nothing to do with irregular endings at all: pluralia tantum are nouns that exist only in plural form because the thing they name is conceived of as inherently having two parts — scissors, trousers, pants, glasses (spectacles), pliers, tweezers. You can't say "a scissor" to mean one pair; English requires "a pair of scissors," treating the plural noun as an uncountable unit modified by "pair." Running in the opposite direction, several nouns that end in -s and look plural are grammatically singular and take a singular verb: news ("the news is on"), physics, mathematics, economics, and measles all originated as, or were reinterpreted from, plural forms but settled into singular agreement once English speakers stopped parsing the -s as a plural marker on an abstract or academic noun. "Politics" sits ambiguously between the two patterns depending on meaning — "politics is a dirty business" (singular, the field) versus "his politics are unclear" (plural, his specific views) — which is one of the few genuinely dual-agreement nouns in the language.
Regularization in progress: technology and brand-name plurals
The same frequency-driven regularization that governs irregular verbs is visible in real time among plurals of recently coined or borrowed nouns, especially in technology. "Virus" is Latin in origin and technically has no classical plural at all (it was a Latin mass noun, like "water"), which hasn't stopped some writers from inventing "viri" or "vira" by false analogy with "cactus"/"cacti" — neither is standard, and "viruses" is simply the correct English plural precisely because the word never had a genuine Latin plural to inherit. "Index" splits by field the same way "formula" does: "indices" in mathematics and finance, "indexes" in everyday and publishing contexts (a book's back-matter index, pluralized). Brand names that have become generic nouns face their own plural questions with no historical precedent to fall back on at all — "Kleenexes," "Xeroxes" — which simply take the regular English -es ending because there's no foreign donor pattern to inherit from in the first place, a reminder that the irregular patterns covered elsewhere on this hub are historical residue, not evidence that irregularity is somehow the default outcome for new nouns entering the language.
"Data" and "media": Latin plurals reinterpreted as singular
"Data" is technically the Latin plural of "datum," and careful scientific and academic style still sometimes treats it that way ("the data are conclusive"), but everyday usage has substantially reinterpreted "data" as an uncountable singular noun on the same pattern as "information" ("the data is conclusive"), and most current style guides now accept both. "Media" is following the identical path a generation behind it: technically the plural of "medium," but increasingly treated as a singular mass noun referring to the press and broadcast industry collectively ("the media is obsessed with this story"), a shift traditionalist style guides still resist more firmly than they've come to resist the parallel shift with "data." Both cases are live examples of exactly the reinterpretation process that produced "agenda" (originally the Latin plural of "agendum," now a fully ordinary singular noun with its own regular plural, "agendas") a few centuries earlier.
How to use this hub
Each noun's own page opens with the correct plural, then walks through which of these historical layers produced it, flags any live spelling debate (octopuses vs. octopi, hoofs vs. hooves), and closes with real example sentences. The full alphabetical list lives on the plural index; come back to this hub instead whenever it's the underlying pattern you're after, not a single lookup.
Pages in this hub (202)
Full index →- Plural of "addendum"
- Plural of "adieu"
- Plural of "aircraft"
- Plural of "alumna"
- Plural of "alumnus"
- Plural of "analysis"
- Plural of "annex"
- Plural of "antenna"
- Plural of "apex"
- Plural of "appendix"
- Plural of "aquarium"
- Plural of "army"
- Plural of "atlas"
- Plural of "attorney-general"
- Plural of "avocado"
- Plural of "axis"
- Plural of "baby"
- Plural of "bacterium"
- Plural of "batch"
- Plural of "beach"
- Plural of "beau"
- Plural of "belief"
- Plural of "bison"
- Plural of "box"
- Plural of "boy"
- Plural of "brother-in-law"
- Plural of "brush"
- Plural of "buffalo"
- Plural of "bureau"
- Plural of "bus"
- Plural of "buzz"
- Plural of "cactus"
- Plural of "cafe"
- Plural of "calf"
- Plural of "cargo"
- Plural of "census"
- Plural of "chateau"
- Plural of "cherry"
- Plural of "chief"
- Plural of "child"
- Plural of "church"
- Plural of "city"
- Plural of "class"
- Plural of "cliff"
- Plural of "codex"
- Plural of "commander-in-chief"
- Plural of "complex"
- Plural of "corpus"
- Plural of "cortex"
- Plural of "country"
- Plural of "court-martial"
- Plural of "crisis"
- Plural of "criterion"
- Plural of "crossroads"
- Plural of "cul-de-sac"
- Plural of "curriculum"
- Plural of "datum"
- Plural of "day"
- Plural of "deer"
- Plural of "diagnosis"
- Plural of "die"
- Plural of "dish"
- Plural of "dress"
- Plural of "duplex"
- Plural of "dwarf"
- Plural of "echo"
- Plural of "editor-in-chief"
- Plural of "elf"
- Plural of "ellipsis"
- Plural of "embargo"
- Plural of "family"
- Plural of "fax"
- Plural of "fish"
- Plural of "fly"
- Plural of "focus"
- Plural of "foot"
- Plural of "formula"
- Plural of "forum"
- Plural of "fox"
- Plural of "fungus"
- Plural of "gas"
- Plural of "genus"
- Plural of "glass"
- Plural of "goose"
- Plural of "gulf"
- Plural of "gymnasium"
- Plural of "half"
- Plural of "halo"
- Plural of "handkerchief"
- Plural of "headquarters"
- Plural of "hero"
- Plural of "hoax"
- Plural of "hoof"
- Plural of "hypothesis"
- Plural of "index"
- Plural of "iris"
- Plural of "key"
- Plural of "kiss"
- Plural of "knife"
- Plural of "lady"
- Plural of "larva"
- Plural of "leaf"
- Plural of "lens"
- Plural of "life"
- Plural of "loaf"
- Plural of "louse"
- Plural of "man"
- Plural of "match"
- Plural of "matrix"
- Plural of "means"
- Plural of "medium"
- Plural of "memo"
- Plural of "memorandum"
- Plural of "millennium"
- Plural of "mongoose"
- Plural of "monkey"
- Plural of "monsieur"
- Plural of "moose"
- Plural of "mosquito"
- Plural of "moth"
- Plural of "mother-in-law"
- Plural of "mouse"
- Plural of "museum"
- Plural of "nebula"
- Plural of "notary-public"
- Plural of "nucleus"
- Plural of "oasis"
- Plural of "octopus"
- Plural of "offspring"
- Plural of "ox"
- Plural of "parenthesis"
- Plural of "party"
- Plural of "passerby"
- Plural of "peach"
- Plural of "penny"
- Plural of "person"
- Plural of "phenomenon"
- Plural of "photo"
- Plural of "piano"
- Plural of "plateau"
- Plural of "platypus"
- Plural of "potato"
- Plural of "puppy"
- Plural of "quiz"
- Plural of "radio"
- Plural of "radius"
- Plural of "reef"
- Plural of "referendum"
- Plural of "rhinoceros"
- Plural of "roof"
- Plural of "runner-up"
- Plural of "salmon"
- Plural of "sandwich"
- Plural of "scarf"
- Plural of "self"
- Plural of "series"
- Plural of "sheep"
- Plural of "shelf"
- Plural of "silo"
- Plural of "sky"
- Plural of "species"
- Plural of "spectrum"
- Plural of "spy"
- Plural of "stadium"
- Plural of "stimulus"
- Plural of "story"
- Plural of "stratum"
- Plural of "studio"
- Plural of "swine"
- Plural of "syllabus"
- Plural of "symposium"
- Plural of "synopsis"
- Plural of "tableau"
- Plural of "tax"
- Plural of "tempo"
- Plural of "thesis"
- Plural of "thief"
- Plural of "tomato"
- Plural of "tooth"
- Plural of "topaz"
- Plural of "tornado"
- Plural of "torpedo"
- Plural of "toy"
- Plural of "trout"
- Plural of "ultimatum"
- Plural of "valley"
- Plural of "vertebra"
- Plural of "vertex"
- Plural of "veto"
- Plural of "video"
- Plural of "virus"
- Plural of "volcano"
- Plural of "vortex"
- Plural of "waltz"
- Plural of "watch"
- Plural of "wharf"
- Plural of "wife"
- Plural of "wish"
- Plural of "witch"
- Plural of "wolf"
- Plural of "woman"
- Plural of "zero"