Irregular Plural Nouns: Definition and List of Examples

The vast majority of nouns in the English language are made plural by adding an “s” or “es” to the end of the word. For example, book changes to books when made plural. However, certain nouns have irregular plurals that do not behave in this standard way. And even though most irregular plural nouns follow a pattern, there are several patterns to watch out for, as you'll see in this list of irregular plural nouns.

irregular plural nouns singular plural irregular plural nouns singular plural
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Irregular Plurals

Certain words do not follow the rules for regular plurals. You'll find some words with no plural form at all. Since there is no way to know which nouns have an irregular plural, you have to memorize them. Explore a few different types of irregular plural nouns without a plural form.

Non-Count Nouns

Non-count nouns are used as collective nouns and have no plural form because they are assumed to be plural. Most abstract nouns are noncount nouns. A few examples of noncountable plural nouns include:

  • hair
  • grass
  • mud
  • dress (when referring to a style of dress, not when referring to a clothing item that hangs in your closet)

If you are talking about multiples of these irregular plurals, you cannot make them plural by adding an “s” or “es” to the end. Instead, you need to make them plural by adding a descriptive phrase.

  • There are many different styles of hair.
  • There are several varieties of grass.
  • There are three different kinds of mud.
  • The ancient people had a few types of styles of dress.

Unchanging Nouns

Certain other nouns have the same singular and plural form. A large number of animals happen to follow this rule. These examples will be spelled the same.

Singular

Plural

aircraft

aircraft

bass

bass

bison

bison

elk

elk

moose

moose

shrimp

shrimp

spacecraft

spacecraft

swine

swine

trout

trout

Irregular Plurals That Change Ending

In addition to non-count nouns and unchanging nouns, several types of irregular plurals follow a pattern in the English language. Explore examples of different endings and how they change, along with irregular plural nouns that change completely.

Nouns With -f or -fe Endings

For most nouns that end in "f" or "fe," you drop the "f" or "fe" and add "ves."

Singular

Plural

knife

knives

wife

wives

half

halves

loaf

loaves

calf

calves

life

lives

Exceptions to this rule include roof and proof, among others. These will get an “s” on the end, as in roofs and proofs.

Nouns Ending in -us

For many words that end in “us,” change the “us” to an “i” (especially if it comes from a Latin word). There are exceptions to this rule, and it’s becoming more acceptable to add “es” instead of changing to “i” in some cases.

Singular

Plural

cactus

cacti

fungus

fungi

hippopotamus

hippopotami (hippopotamuses is acceptable)

octopus

octopi (octopuses is acceptable)

syllabus

syllabi

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Nouns With -o Endings

For nouns that end in “o,” you add either “s” or “es.” Generally, most nouns ending in “o” just add “s” to make the plural, especially if there's a vowel before the final “o.” However, you'll also find words that work with both endings.

irregular plural noun tomato tomatoes

Singular

Plural

banjo

banjos or banjoes

flamingo

flamingos or flamingoes

potato

potatoes

studio

studios

tomato

tomatoes

zoo

zoos

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Words With -is Endings

For many words that end in “is,” change the “is” to an “es.” Check out a few examples.

Singular

Plural

axis

axes

crisis

crises

hypothesis

hypotheses

oasis

oases

thesis

theses

Nouns With -um Endings

Nouns that end in "um" often become plural by changing “um” to “a.” See how this looks in action here.

Singular

Plural

bacterium

bacteria

curriculum

curricula

datum

data

medium

media

stratum

strata

Nouns With -ix Ending

Another irregular plural noun ending that changes is “ix.” In Greek and Latin words, this will change to “ces” or “xes.”

Singular

Plural

appendix

appendixes or appendices

crucifix

crucifixes

matrix

matrices or matrixes

Words That Change Form

Certain words do not add a letter to the end to become plural. Instead, these irregular plurals change the word itself. These words simply need to be memorized.

Singular

Plural

die

dice

foot

feet

goose

geese

man

men

mouse

mice

ox

oxen

person

people

tooth

teeth

Regular Plurals

Now that you’ve seen irregular plural nouns, it’s important to review how regular plural nouns work. The general rule for making a noun plural is that if the word ends in "s," "x," "z," "ch" or "sh," add an "es." Review a few examples of what this might look like.

Singular

Plural

mess

messes

box

boxes

patch

patches

dish

dishes

buzz

buzzes

Add an S

For all other non-irregular nouns, simply add an "s" to the end of the word.

Singular

Plural

cat

cats

dog

dogs

yard

yards

Exceptions to Regular Plural Rules

An exception to the add an "es" rule is if the "ch" ending is pronounced with a /k/ sound, you add "s" rather than "es."

Singular

Plural

epoch

epochs

monarch

monarchs

stomach

stomachs

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Vowel Endings

If the word ends in a consonant (all letters except a, e, i, o, u) plus "y," then change the "y" to an "i" and add the letters "es."

Singular

Plural

baby

babies

candy

candies

daisy

daisies

Understanding Irregular Plural Nouns

The best way to learn and understand irregular plurals is to practice speaking the English language, to read a great deal, to pay attention to words and phrases that you see and hear, and to assemble a list of words with irregular plurals so you can begin to understand how to make each noun plural correctly. Looking for more fun grammar rules? Check out definite and indefinite articles. Is it “a,” “an” or “the”? Find out!