What Is an Irregular Plural Noun? Usage Guide and Examples

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What do James Dean and moose have in common? They don’t like to follow the rules. While James Dean may have been a rebel without a cause, moose (and deer, and mice, and octopuses) refuse to follow standard grammar rules. But no matter how cool you look on a motorcycle, you’ve got to know how to spell irregular nouns — because nothing’s cooler than proper spelling.

What Is an Irregular Plural Noun?

For most plural nouns in English, adding "s" or "es" to the end of the word changes a singular noun into a plural noun (friend becomes friends, wristwatch becomes wristwatches, and so on). But with irregular plural nouns, that’s not the case.

Examples of irregular plural nouns include:

  • parties
  • mice
  • moose
  • scissors
  • men
  • wives
  • tomatoes

Irregular plural nouns either change their endings (such as party to parties) or stay the same as their singular forms (such as moose to moose). It may seem like they’re just breaking grammar rules, but really, irregular plural nouns are just following different spelling rules.

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List of Irregular Plural Nouns

Just because they’re called irregular doesn’t mean these plural nouns are uncommon. In fact, you’ll find many of them in your everyday speech.

charts showing irregular plural noun examples for different rules

Irregular Plural Nouns Printable 22

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Rules for Changing Irregular Plural Nouns

Many irregular nouns change their endings when they move from singular to plural. Once you know how each noun’s spelling changes, you’ll make fewer spelling mistakes.

Irregular Plural Nouns That End in "ies"

If the word ends in a consonant plus "y," then change the "y" to an "i" and add the letters "es.”

Singular Noun

Plural Noun

Example Sentence

baby

babies

Four babies were born this week.

candy

candies

Those candies are too sour.

daisy

daisies

We ran through a field of daisies.

lady

ladies

Three old ladies walked by.

party

parties

How many parties are you attending?

When a word ends in a vowel and “y” (such as monkey or day), you just add an “s” to the end (monkeys, days).

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Irregular Plural Nouns That End in "ves"

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

Singular Noun

Plural Noun

Example Sentence

calf

calves

Baby calves stay near their mothers.

half

halves

Two halves make a whole.

knife

knives

These knives are too dull.

life

lives

Do cats really have nine lives?

loaf

loaves

I made two loaves of banana bread.

wife

wives

Henry VIII had six wives.

When a noun ends in a double vowel and an “f” (such as roof or proof), it doesn’t change to “ves” in the plural form. Instead, just add an “s” to the end (roofs, proofs).

Irregular Plural Nouns That End in "i"

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 — especially if the word has a Greek root.

Singular Noun

Plural Noun

Example Sentence

cactus

cacti

We replaced our rose bushes with cacti.

fungus

fungi

Mushrooms and mold are both fungi.

hippopotamus

hippopotami (hippopotamuses is acceptable)

Both hippopotami love eating pumpkins.

octopus

octopi (octopuses is acceptable)

Three blue octopi swam by us.

syllabus

syllabi

There’s a stack of syllabi on the teacher’s desk.

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Irregular Plural Nouns That End in "a" or "ia"

Another Latin spelling convention turns singular nouns that end in "um" into plural nouns that end in “ia.”

Singular Noun

Plural Noun

Example Sentence

bacterium

bacteria

Millions of bacteria infected the injury.

curriculum

curricula

Teachers organize their curricula before school begins.

datum

data

Have you examined all the data?

medium

media

I create art in many different media.

stratum

strata

There are four social strata in this society.

Irregular Plural Nouns That End in "es"

Some irregular plural nouns do end in "es" — but you don't just add it to their endings. For many words that end in “is,” change the “is” to an “es.” These are also pronounced differently (ees at the end of each word, not es)

Singular Noun

Plural Noun

Example Sentence

axis

axes

All planets rotate on axes.

crisis

crises

Two crises were happening at once.

diagnosis

diagnoses

The patient has at least five diagnoses.

hypothesis

hypotheses

Scientists have several hypotheses.

oasis

oases

Day spas can be oases in a busy day.

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Irregular Plural Nouns That Change Completely

Parties, bacteria, and cacti at least follow their own rules. But certain irregular plural nouns, such as children or teeth, don’t follow any grammatical rules at all. The only way to get them right is to memorize them.

Singular Noun

Plural Noun

Example Sentence

child

children

How many children do you have?

die

dice

Roll both dice on your next turn.

foot

feet

Both feet hurt after the long hike.

goose

geese

At least ten geese chased me around.

man

men

Four men worked on the project.

mouse

mice

Are there any mice in your walls?

ox

oxen

It took eight oxen to pull the heavy cart.

person

people

How many people came to the party?

tooth

teeth

Lily lost three teeth this weekend.

Irregular Plural Nouns That Don’t Change at All

Just as you were mastering the irregular plural nouns that change their endings, here come the nouns that don’t change at all. The good news is, you only need to learn one spelling — the bad news is, there’s no rule about which words follow this rule.

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Uncountable Nouns

Uncountable nouns don’t have plural forms. They usually describe an uncountable quantity of something (such as air or love).

Singular Noun

Plural Noun

Example Sentence

hair

hair

She cut her hair before the dance.

grass

grass

Did you water the grass?

happiness

happiness

All I care about is your happiness.

independence

independence

Teenagers value their independence.

mud

mud

Please don’t stomp in the mud.

Unchanging Nouns

Many nouns have the same singular and plural forms, especially species of animals. You can only tell that they’re plural by reading the context clues in the rest of the sentence. 

Singular Noun

Plural Noun

Example Sentence

aircraft

aircraft

Four aircraft zoomed overhead.

bison

bison

Many bison roam these prairies.

deer

deer

Three deer crossed the road.

fish

fish

How many fish did you catch?

moose

moose

Both moose stopped to drink from the lake.

spacecraft

spacecraft

Three spacecraft launched on the same day.

swine

swine

Look at all the swine at this farm.

trout

trout

We caught several trout this morning.

Irregular Plural Noun Quiz

Can you change the irregular noun in these sentences to its plural irregular form?

  1. How many (loafs, loaves) of bread did you bring to dinner?
  2. We bought six (shrimp, shrimps) for our aquarium.
  3. The president deals with many (crisises, crises) at a time.
  4. Please tell the (childs, children) to come in.
  5. Our family has been on many (journies, journeys) together.
  6. Ten new (spacecraft, spacecrafts) are flying to Mars.
  7. You ate both (halfs, halves) of the birthday cake?
  8. Sheila brushed her (hair, hairs) before the party.

Answer Key for Irregular Plural Noun Quiz

Not many people (not persons) can find all the correct irregular plural nouns above. Did you?

  1. How many (loafs, loaves) of bread did you bring to dinner?
  2. We bought six (shrimp, shrimps) for our aquarium.
  3. The president deals with many (crisises, crises) at a time.
  4. Please tell the (childs, children) to come in.
  5. Our family has been on many (journies, journeys) together.
  6. Ten new (spacecraftspacecrafts) are flying to Mars.
  7. You ate both (halfs, halves) of the birthday cake?
  8. Sheila brushed her (hair, hairs) before the party.