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, apple, house, table, cat, and boss are just some of the many words that become plural with the simple addition of an “s” or “es” (books, apples, houses, tables, cats, and bosses, respectively).

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 different patterns to watch out for, as you'll see in our list of examples.


Irregular Plurals

Certain words do not follow the rules for regular plurals. There are some common types of irregular plural nouns that occur, and some words simply have no plural form at all. While it is useful to memorize the common irregular plurals, for many words you simply have to know and understand that it’s an irregular plural as a result of speaking and hearing English.

Noncount Nouns

Noncount nouns, also called collective nouns, have no plural form because they are assumed to be plural. Most abstract nouns are noncount nouns. Some examples are:

  • 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 multiple varieties or types 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. For example:

  • 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.

  • Deer
  • Fish
  • Bison
  • Moose
  • Elk
  • Swine
  • Shrimp
  • Bass
  • Trout
  • Aircraft
  • Spacecraft

Other Irregular Plurals

In addition to noncount nouns and unchanging nouns, there are several different types of irregular plurals that 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."

  • 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” to the end, as in roofs and proofs.

“Us” Endings in Nouns

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.

  • Cactus = cacti
  • Fungus = fungi
  • Syllabus = syllabi
  • Octopus = octopi (it can also be octopuses)
  • Hippopotamus = hippopotami (it can also be hippopotamuses)

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.”

  • Zoo = zoos
  • Studio = studios
  • Tomato = tomatoes
  • Potato = potatoes

Some words ending in “o” can be spelled either way, like:

  • Banjo = banjos or banjoes
  • Flamingo = flamingos or flamingoes

Words With “Is” Endings

For many words that end in “is,” change the “is” to an “es.” This will look like:

  • Hypothesis = hypotheses
  • Oasis = oases
  • Crisis = crises
  • Axis = axes
  • Crisis = crises
  • 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.

  • Bacterium = bacteria
  • Medium = media
  • Curriculum = curricula
  • Datum = data
  • 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.” This will look like:

  • Appendix = appendixes or appendices
  • Matrix = matrices or matrixes
  • Crucifix = crucifixes

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. Some examples include:

  • Man = men
  • Foot = feet
  • Tooth = teeth
  • Goose = geese
  • Mouse = mice
  • Die = dice
  • Person = people
  • Ox = oxen

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 these examples:

  • Mess = messes
  • Box = boxes
  • Patch = patches
  • Dish = dishes
  • Buzz = buzzes

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

  • Stomach = stomachs
  • Epoch = epochs
  • Monarch = monarchs

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"

  • Baby = babies
  • Candy = candies
  • Daisy = daisies

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

  • Cat = cats
  • Dog = dogs
  • Yard = yards

Understanding Irregular Plural Nouns

The best ways to learn and understand irregular plurals are 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!