Understanding Irregular Plural Nouns (List, Examples, Worksheet)

An irregular noun undergoes more dramatic changes than a regular noun to form a plural noun. Irregular plural nouns are not formed by simply appending -s or -es to the end of the noun. There are additional variations.

For example, woman in the singular form becomes women in the plural form. The plural of wolf is wolves, and not wolfs.

What are irregular nouns?

Irregular nouns do not follow a rule set to form plurals—it’s best to memorize and practice them. However, some irregular nouns have predictable pluralizations because they follow a pattern in terms of the words they end with.

Some examples of irregular singular nouns are nouns ending with -f, -y, or -fe. For example, Wolf, Life, and Tray.

We use many irregular plural nouns in our daily lives without even realizing it.

Difference between Regular Plural Nouns

A regular noun becomes plural by adding -s or -es at the end of the word.

Example 1:

A: Ron has a math book.

B: Ron has three math books.

In example A, book is a regular noun in a singular form. In example B, by adding -s at the end of the word, book turns books. Therefore, books is a regular plural noun.

Example 2:

A: There was an actor waiting in the green room.

B: There were actors waiting in the green room.

In example A, actor is a regular noun in a singular form. In example B, by adding -s at the end of the word, actor becomes actors. Therefore, actors is a regular plural noun.

To determine which regular nouns end with -es in their plural forms, check if the ending letters of the singular noun are -x, -ch, -sh, -z, -s, or -ss.

Example 3:

A: A fox was lying on the grass.

B: Two foxes were lying on the grass.

In example A, fox is a regular noun in a singular form, ending with the letter -x. In example B, by adding -es at the end of the word, fox becomes foxes. Therefore, foxes is a regular plural noun.

Example 4:

A: Lisa borrowed a blue watch from her grandmother.

B: Lisa borrowed blue watches from her grandmother.

In example A, watch is a regular noun in a singular form, ending with the letters -ch. In example B, by adding a -es at the end of the word, watch becomes watches. Therefore, watches is a regular plural noun.

Irregular nouns, on the other hand, have unique or different rules for becoming plural nouns. They don’t become plural by adding a -s or -es at the end of the noun.

Some possible cases to determine an irregular noun’s plural form are based on:

the ending alphabet/s of the irregular noun (e.g. for nouns ending with -f, replace -f with -ves).
the vowels of the irregular noun (e.g., the -oo in goose becomes -ee in its plural form, geese).

There are many irregular nouns whose plural forms are difficult to recall (unless you memorize them or look them up in the dictionary).

For example, a person in a singular form becomes people in the plural form.

Example:

A: The mouse ate all the cheese.

B: The mice ate all the cheese.

In example A, mouse is an irregular noun. To form the plural of mouse, the entire word is changed dramatically. In example B, the -ous in the mouse is replaced with -ic. Therefore, the irregular plural of mouse becomes mice.

Relationship between Regular and Irregular Plural Nouns

Regular and irregular plural nouns both serve the same function—indicating more than one name, place, animal, or thing, depending on the referred noun.

E.g. One tree, many trees. One fox, many foxes. One cake, many cakes.

Regular and irregular nouns can coexist in the same sentence in both singular and plural forms and still make sense. It’s important, though, to use the correct endings for each of these nouns.

For example, Ron had two pencils and one pen in his school bag. He had five books on each of his bookshelves.

Here, pen and school bag are singular nouns, pencils and books are regular plural nouns, and bookshelves is an irregular plural noun.

Pencils have a -s at the end, indicating that there is more than one of them (in our case, two pencils).

Bookshelves have a-ves at the end instead of a -f, indicating that there is more than one bookshelf.

Irregular Plural Noun Rules

The rules for irregular plural nouns are more varied than regular noun rules. While not every irregular noun has a pluralization rule, there are a few types of irregular nouns that do.

Rule #1: For nouns ending with -f, replace -f with -ves

To form plurals of nouns ending with the letter -f, replace -f with -ves at the end of the word.

Similarly, to form plurals of nouns ending with the letters -fe, replace -fe with -ves at the end of the word.

Below are some irregular nouns that follow this rule.

Singular form (ending with -f)	Plural form (ending with -ves)
Wolf	Wolves
Leaf	Leaves
Calf	Calves
Loaf	Loaves
Shelf	Shelves
Half	Halves
Self	Selves
Thief	Thieves
Elf	Elves
Bookshelf	Bookshelves
Interleaf	Interleaves
Underleaf	Underleaves
Werewolf	Werewolves

Example 1:

A: He had treasured his grandmother’s clothes on the blue shelf.

B: He had treasured his grandmother’s clothes on the blue shelves.

In example A, the singular form, shelf, is mentioned. In example B, the plural form of shelf—shelves—is mentioned.

Example 2:

A: The thief escaped from the room.

B: The thieves escaped from the room.

In example A, the singular form, thief, is mentioned. In example B, the plural form of thief—thieves—is mentioned.

Rule #2: For nouns ending in -o, add -es at the end of the noun.

Singular form (ending with -o)	Plural form (ending with -es)
Mango	Mangoes
Tornado	Tornadoes
Domino	Dominoes
Potato	Potatoes
Tomato	Tomatoes
Hero	Heroes
Zero	Zeroes
Mosquito	Mosquitoes
Echo	Echoes
Buffalo	Buffaloes

Example 1:

A: A mosquito troubled an elephant in the jungle.

B: The mosquitoes troubled an elephant in the jungle.

In example A, the singular form, mosquito, is mentioned. In example B, the plural form of mosquito—mosquitoes—is mentioned.

Example 2:

A: Patrick heard the echo of an old woman in the church.

B: Patrick heard echoes of an old woman in the church.

In example A, the singular form, echo, is mentioned. In example B, the plural form of echo—echoes—is mentioned.

Rule #3 For nouns ending in -y form plural by replacing -y with -ies

Singular form (ending with -y)	Plural form (ending with -ies)
Lady	Ladies
Candy	Candies
Enemy	Enemies
Body	Bodies
Strawberry	Strawberries
Pony	Ponies
Puppy	Puppies
Story	Stories
Baby	Babies
Army	Armies
Firefly	Fireflies
Lorry	Lorries
Bunny	Bunnies
Fairy	Fairies

Example 1:

A: At night, Rachel dreamt of a fairy who would take her to a fairyland.

B: At night, Rachel dreamt of fairies who would take her to a fairyland.

In example A, the singular form, fairy, is mentioned. In example B, the plural form of fairy—fairies—is mentioned.

Example 2:

A: By evening, the army proceeded toward the base camp.

B: By evening, the armies proceeded toward the base camp.

In example A, the singular form, army, is mentioned. In example B, the plural form of army—armies—is mentioned.

Rule #4: For nouns with changing vowels

Singular form	Plural form
Man	Men
Woman	Women
Goose	Geese
Foot	Feet
Tooth	Teeth

Example 1:

A: Mike’s tooth ached terribly after eating jelly candies.

B: Mike’s teeth ached terribly after eating jelly candies.

In example A, tooth is an irregular noun in the singular form. To form the plural of tooth, the vowels of the noun are changed. So, -oo becomes -ee. In example B, teeth is an irregular plural noun.

Example 2:

A: There is a woman waiting in the office, asking for Mr. Ben.

B: There are women waiting in the office, asking for Mr. Ben.

In example A, woman is an irregular noun in singular form. To form the plural of woman, the vowel of the noun is changed.* So, -a becomes -e. In example B, women is an irregular plural noun.

*woman has two vowels—o and a—but only a is changed in the plural form.

Rule # 5: For Nouns that change dramatically

The plural form of such nouns is difficult to predict because it does not follow a specific pattern. When in doubt, look up the word in the dictionary.

Singular form	Plural form
Person	People
Mouse	Mice
Child	Children
Ox	Oxen
Die	Dice
Louse	Lice

Example 1:

A: She is the child of God.

B: They are the children of God.

In example A, child is an irregular noun in singular form. The plural form of child is stated in example B, i.e., children.

Example 2:

A: Matt had an ox and a hen in his farm.

B: Matt had oxen and hens in his farm.

In example A, ox is an irregular noun in the singular form. The plural form of ox is stated in example B, i.e., oxen.

Rule #6 For nouns that remain unchanged

Singular form	Plural form
Shrimp	Shrimp
Wheat	Wheat
Sheep	Sheep
Bison	Bison
Fish	Fish
Aircraft	Aircraft
Hair	Hair
Trout	Trout
Swine	Swine
Spacecraft	Spacecraft
Elk	Elk
Moose	Moose

Example 1:

A: Uncle Vernon ate a tasty shrimp for dinner.

B: Uncle Vernon ate a plate full of tasty shrimp for dinner.

In example A, shrimp is an irregular noun. In example B, the plural form of shrimp is also shrimp. Here, the singular and plural forms of the irregular noun are the same.

Example 2:

A: The engineer designed the prototype for a spacecraft and submitted it to NASA.

B: The engineer designed the prototype for the spacecraft and submitted them to NASA.

In example A, spacecraft is an irregular noun. In example B, the plural form of spacecraft is also spacecraft. Here, the singular and plural forms of the irregular noun are the same.

Irregular Plural Nouns from Latin and Greek

Because of their origins, many irregular noun pluralizations are difficult to predict. Many of these nouns are derived from Latin or Greek. Mentioned below is a list of such nouns in their respective categories.

Final a becomes -ae, or just add -s

For singular irregular nouns ending with -a, replace -a with -ae at the end of the word to form its plural.

Singular form (ending with -a)	Plural form (ending with -ae)
Alga	Algae
Larva	Larvae
Vertebra	Vertebrae
Formula	Formulae
Alumna	Alumnae

Example 1:

A: The egg develops into a larva.

B: The larvae develop from the eggs.

In example A, larva is an irregular noun in the singular form. In example B, -e is added at the end of the noun. Therefore, the plural form of larva is larvae.

Example 2:

A: “Memorize the formula before you attend the math class tomorrow,” commanded the teacher.

B: “Memorize the formulae before you attend the math class tomorrow,” commanded the teacher.

In example A, formula is an irregular noun in the singular form. In example B, -e is added at the end of the noun. Therefore, the plural form of formula is formulae.

Exceptions: Some irregular nouns that end in ‘a’ in their singular form become plurals by adding -s at the end of the noun.

Singular form (ending with -a)	Plural form (ending with -s)
Abaca	Abacas
Idea	Ideas
Koala	Koalas

Final -ex or -ix becomes -ices

In Latin, singular irregular nouns ending in -ex or -ix are pluralized by replacing -ex or -ix with -ices at the end of the word.

Singular form (ending with -ex or -ix)	Plural form (replace with -ices)
Appendix	Appendices
Matrix	Matrices
Vertex	Vertices
Codex	Codices
Textrix	Tectrices
Cortex	Cortices

Note: There are some irregular nouns ending in -x that take the rule of regular nouns or identical nouns. For example, the plural of vernix is also vernix. Affix in the singular form becomes affixes in the plural form.

Final -is becomes -es

In its Latin form, singular irregular nouns ending with -is are replaced with -es instead of -is to form its plural.

Singular form (ending with -is)	Plural form (replace -is with -es)
Basis	Bases
Oasis	Oases
Thesis	Theses
Crisis	Crises
Diagnosis	Diagnoses
Axis	Axes
Hypothesis	Hypotheses

Final -um becomes -a, or just add -s

Many of the below words are inspired by Latin and Greek words and are mostly used in the mathematical or scientific context.

Singular form (ending with -um)	Plural form (replace -um with -a)
Datum	Data
Spectrum	Spectra
Memorandum	Memoranda
Bacterium	Bacteria
Criterium	Criteria
Curriculum	Curricula
Phenomenon	Phenomena
Sporangium	Sporangia
Perichondrium	Perichondria
Platinum	Platina
Equilibrium	Equilibria
Aquarium	Aquaria
Cerebrum	Cerebra

Exception: Some irregular nouns ending with -um form plurals by adding a -s at the end of the noun.

Singular form (ending with -um)	Plural form (ending with -s)
Slum	Slums
Gum	Gums
Checksum	Checksums
Plum	Plums
Drum	Drums

Final -us becomes -i or -era

Some of the mentioned words also form plurals by adding -es at the end of the word. This plural form is its anglicized version.

For example, focus in its singular form is focuses in its plural form. Similarly, the plural form of octopus is also octopuses.

Singular form (ending with -us)	Plural form (ending with -i or -era)
Fungus	Fungi
Genus	Genera
Cactus	Cacti
Locus	Loci
Onus	Onera
Abacus	Abaci
Alumnus	Alumni
Octopus	Octopi
Radius	Radii
Nucleus	Nuclei

Exceptions: Some irregular nouns ending with -us become plurals by adding -es at the end of the word.

Singular form (ending with -us)	Plural form (adding -es)
Lotus	Lotuses
Focus	Focuses

Final -us remains unchanged in the plural

Singular form (ending with -us)	Plural form (ending with -us)
Status	Status
Meatus	Meatus
Apparatus	Apparatus

Final -on becomes -a

The plural forms of these words are widely used as compared to their singular counterparts.

Singular form (ending with -on)	Plural form (ending with -a)
Phenomenon	Phenomena
Automaton	Automata
Criterion	Criteria

Irregular plural nouns from other languages

Some irregular nouns taken from the Italian language have different pluralizations. For example, a group of words, irrespective of what letter/s they end with, add -s at the end to form a plural.

Below are some examples.

Singular form	Plural form
Cello	Cellos
Ballerina	Ballerinas
Duo	Duos
Logo	Logos
Trombone	Trombones
Violin	Violins
Sonata	Sonatas
Opera	Operas

Tips for using irregular plural nouns

Tip #1

Use -ces for the casual form of irregular nouns ending in -ex or -ix, and -xes for the scientific or mathematical form.

For example, use indices in the casual form and indexes in the formal setting as the plural form of index.

Example:

The psychology book contains two indexes, three appendixes, and four glossaries.

The words indexes and appendixes are pluralized here, with -es added at the end.

Tip #2

For the names of animals, their irregular plurals are likely to be identical plurals. Look up the dictionary before you add -s or -es at the end of such nouns.

For example, deer in singular form is also deer in plural form. Similarly, sheep in singular form is also sheep in plural form.

Tip #3

There are only seven mutant plurals in English. These plurals change vowels when converting from singular to plural.

List of mutant plurals:

Foot
Woman
Man
Goose
Louse
Moose

Example:

A: There is a moose playing in the open field.

B: There are mice playing in the open field.

In example A, moose is an irregular (mutant), singular noun. In example B, mice is an irregular plural noun.

Tip #4

There are only four irregular nouns in English that add -en at the end of the word to form a plural.

Singular form	Plural form (ending with -en)
Child	Children
Ox	Oxen
Sister	Sistren
Brother	Brothren

Singular and plural form ending in "en" chart — Singular and plural form ending in “en” chart

Tip #5:

Some irregular nouns are always in their plural form.

Examples:

Scissors
Glasses
Binoculars
Sunglasses
Goggles
Shorts
Thanks
Headphones
Tweezers
Belongings

Use a quantifier to distinguish between the noun’s singular and plural counterparts.

Example:

One pair of scissors. Two pairs of scissors

A pair of tweezers, five pairs of tweezers.

In cases where adding a quantifier won’t make sense, use a verb or pronouns (it, them, etc.) to indicate whether the noun is singular or plural.

Exercise:

In the following examples, figure out whether the highlighted noun is in the singular form or plural form.

June wore trousers all day.

Oh my god! I lost my pair of lenses.

Thanks for your gift, Chloe.

Make sure you dry your clothes before ironing them.

Joey took away all his belongings before leaving Chandler’s house.

Tip #6

Irregular nouns that end in -y and are preceded by a consonant become plural by changing the -y to -i and then adding -es.

Example:

For city in the singular form, change the ending letter -y to -i (Citi). Then, add -es at the end. The resulting plural noun is cities.

Another similar example is country becoming countries.

Tip #7

If an irregular noun ending with y is preceded with a vowel, simply add -s at the end of the word.

Example:

Monkey in the singular form becomes monkeys in the plural form.

Donkey in the singular form becomes donkeys in the plural form..

Tip #8

To form plurals of nouns ending with -f, we replace -f with -ves. This is because appending a -s at the end of -f results in -fs, that sounds like -ves.

Shelf, for example, sounds like shelves if it is written as shelfs.

The plural form shelves was introduced to make the English language more convenient and cut down on the difficulty of pronouncing shelfs.

However, there is an exception. Not all nouns ending with -f in their singular form replace -f with -ves during pluralization. Instead, they form plurals by adding -s at the end of the noun.

Singular form (ending with -f)	Plural form (ending with -s)
Brief	Briefs
Chef	Chefs
Motif	Motifs
Roof	Roofs

Singular form ending in "f" example — Singular form ending in “f” example

Example 1:

A: The chef worked in an old restaurant for years.

B: The chefs worked in an old restaurant for years.

In example A, chef is singular in the first statement. In example B, its plural form, chefs is mentioned.

Example 2:

A: The roof was leaking.

B: The roofs were leaking.

In example A, roof is singular in the first statement. In example B, its plural form, roofs is mentioned.

Tip #9

Some irregular nouns that end in ‘o’ in their singular form become plurals by adding an -s at the end of the noun.

Singular form (ending with ‘o’)	Plural form (ending with ‘s’)
Tango	Tangos
Amigo	Amigos
Burrito	Burritos
Taco	Tacos

Singular form ending in "o" chart — Singular form ending in “o” chart

Example 1:

A: Monica made a taco filled with vegetables and cheese.

B: Monica made tacos filled with vegetables and cheese.

In example A, taco is singular in the first statement. In example B, its plural form, tacos is mentioned.

Example 2:

A: Slice the mango and store it in an airtight container.

B: Slice the mangoes and store them in an airtight container.

In example A, mango is an irregular singular noun. By simply adding -es at the end of the word, mango becomes mangoes. Therefore, in example B, mangoes is an irregular plural.

Tip #10

Some irregular nouns that end in ‘o’ in their singular form become plurals by adding an -s at the end of the noun. It’s best to memorize them to avoid any further confusion.

Singular form (ending with -y)	Plural form (ending with -s)
Trolley	Trolleys
Journey	Journeys
Kidney	Kidneys
Key	Keys
Toy	Toys

Singular form ending in "y" chart — Singular form ending in “y” chart

Example 1:

A: Chelsea decided to donate her kidney after her death.

B: Chelsea decided to donate her kidneys after her death.

In example A, kidney is an irregular singular noun. By simply adding -s at the end of the word, kidney becomes kidneys. Therefore, in example B, kidneys is an irregular plural.

Example 2:

A: Vani has a toy that is bright and blue.

B: Vani has toys that is bright and blue.

In example A, toy is an irregular singular noun. By simply adding -s at the end of the word, toy becomes toys. Therefore, in example B, toys is an irregular plural.

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About the author

Dalia Y.: Dalia is an English Major and linguistics expert with an additional degree in Psychology. Dalia has featured articles on Forbes, Inc, Fast Company, Grammarly, and many more. She covers English, ESL, and all things grammar on GrammarBrain.