How to Form Plural Nouns in English: Irregular Plural Nouns

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Nouns are traditionally defined as “words that name people, places, things, and ideas.” The following article lists and explains the rules for forming the plurals of irregular nouns in the English language.

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Irregular Plural English Nouns

Unlike regular English nouns for which the plural morphological suffix is either -s or -es, irregular English nouns require vowel changes, consonant changes, or suffixation. For some common English nouns of Old English origin, the vowel undergoes an ablaut or vowel sound change. For example, the following chart identifies the singular and plural forms of some common irregular English nouns of Old English origin:

Singular – Plural
foot – feet
louse – lice
man – men
mouse – mice
person – people (also consonant sound change)
tooth – teeth
woman – women

For some other common English nouns of Old English origin, the plural morphological suffix is -en or -n. For example, the following chart identifies the singular and plural forms of some other common (and dialectal) irregular English nouns of Old English origin:

Singular – Plural
brother – brethren/brothers (archaic)
child – children
cow – kine/cows (archaic)
eye – eyen/eyes (dialectal)
ox – oxen
house – housen/houses (dialectal)
shoe – shoon/shoes (dialectal)

For other common English nouns often of Old English origin and referring to groups of animals, the plural form is identical to the singular form. For example, the following chart identifies the singular and plural forms of some more irregular English nouns:

Singular – Plural
bison – bison
deer – deer
moose – moose
offspring – offspring
salmon – salmon
sheep – sheep
species – species
trout – trout

Irregular Plural Foreign Nouns

Unlike the plural forms of nouns of English origin, the plurals of nouns borrowed as loanwords from foreign languages often conserve the plural form from the original language. If the noun is of Latin origin and ends in a, change the a to an ae. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in a:

Singular – Plural
alumna – alumnae
formula – formula

If the noun is of Latin origin and ends in ex or ix, change the ex or ix to ices. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in ex and ix:

Singular – Plural
index – indices
matrix – matrices
vertex – vertices

If the noun is of Latin origin and ends in is, change the is to an es. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in es:

analysis – analyses
axis – axes
crisis – crises
testis – testes
thesis – theses

If the noun is of Latin origin and ends in on, change the on to an a. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in on:

automaton – automata
criterion – criteria
phenomenon – phenomena

If the noun is of Latin origin and ends in um, change the um to an a. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in um:

addendum – addenda
datum – data
medium – media
memorandum – memoranda
millennium – millennia

If the noun is of Latin origin and ends in us, change the us to an i, era, ora, or es. For example, the following chart identifies the singular and plural forms of Latin loanwords ending in us:

alumnus – alumni
cactus - cacti
corpus – corpora
census – censuses
focus – foci
fungus – fungi
genus – genera
radius – radii
syllabus – syllabi
uterus – uteri
viscus – viscera

If the noun is of Greek origin and ends in ma, add the suffix -ta to the end of the word. For example, the following chart identifies the singular and plural forms of Greek loanwords ending in ma:

dogma – dogmata
schema – schemata
stigma – stigmata
stoma – stomata

If the noun is of French origin and ends in eau, add a silent -x suffix to the end of the word. For example, the following chart identifies the singular and plural forms of French loanwords ending in eau:

beau – beaux
bureau – bureaux
château – châteaux

If the noun is of Hebrew origin , add the suffix -im or -ot to the end of the word. For example, the following chart identifies the singular and plural forms of Hebrew loanwords:

cherub – cherubim
matzah – matzot
seraph – seraphim

Like with regular English nouns ending in o, the current trend for spelling the pronouncing the plurals of loanwords from foreign languages seems to be moving in the direction of adding only the morphological suffix -s, particularly in the case of uncommon or infrequent nouns.

Printable Download

For a printable reference study sheet of the morphological, spelling, and pronunciation rules for forming plurals of irregular nouns in English, please download the supplement to this article Forming Plural Nouns in English: Rules for Plural Nouns Reference Sheet .

This post is part of the series: How to Form Plural Nouns in English

The following two part series lists the morphological, spelling, and pronunciation rules for forming the plurals of regular and irregular nouns in English. Part one explains the rules for regular English nouns. Part two explains the rules for irregular English nouns.