Most nouns can change from singular to plural with the simple addition of an -s or an -es at the end of the noun. However, some nouns choose to be difficult, and can have a wide range of different endings when changed to their plural form! These are called irregular nouns.

Read on to learn more about irregular plural nouns and to familiarize yourself with some of these common rule-breakers.  

When you’re ready, test yourself with a quiz and practice with our high-quality, standards-aligned questions here.

The Basics of Irregular Plural Nouns 

What is a regular noun? 

A regular noun can be made plural by simply adding -s or -es to the end of the word. For example, a regular noun like pickle becomes plural by adding an -s to the end of the word, creating the plural noun pickles. 

It would make our lives as writers so much easier if all nouns followed this simple rule, but some nouns like to be rebels, especially irregular nouns. 

What is an irregular plural noun?

An irregular plural noun is a noun that becomes plural in a way other than adding -s or -es to the end. For example, an irregular noun like mouse changes into the plural noun mice. 

Another example is the noun thief which becomes thieves when there is more than one robber involved in a heist. 

Or, nouns like sheep or scissors look exactly the same whether these nouns are referring to one or one hundred wooly sheep or sharp scissors. 

What is the relationship between regular and irregular plural nouns? 

Regular and irregular noun endings are both used by writers to show whether a noun is plural. Although the endings of these nouns are very different from one another, their purpose is the same. 

For example, both regular and irregular nouns can exist within the same sentence and make sense to the reader when the correct endings are used. 

Take a look at this sentence that uses both regular and irregular plural nouns: 

Joe’s dad bought two bikes for his children over the weekend. 

• Bikes is a regular plural noun that uses an -s ending to show that multiple bikes were purchased. 
• Children is an irregular plural noun that uses an -ren ending to show that Joe’s dad has more than one child. 

How do you use irregular plural nouns? 

Writers use both regular and irregular plural nouns so often that you may use irregular nouns without even realizing it. 

If you grew up speaking the English language, you instinctively know that it would sound silly to order “twenty shrimps” at Red Lobster. You know that the plural of shrimp is, well, shrimp! And adding an -s to the end to make it plural just doesn’t sound right. 

However, there has to be a better way to understand these irregular nouns than simply explaining that it “doesn’t sound right”. 

Below, there are several tips to help you better understand these nouns by placing them into manageable categories.

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5 Tips for Understanding Irregular Nouns

Here are some important tips to help you understand irregular nouns:

Tip #1. If the noun ends in -us, change the ending to -i to make an irregular plural noun

• For example, a biologist might compare the nuclei of several different cells rather than a single nucleus. 
• Or, when you graduate from high school, you are considered an alumnus, but everyone in your graduating class as a group would be referred to as alumni. 

Tip #2. If the noun ends in -f or -fe, change the ending to -ves to make an irregular plural noun

• For example, a single leaf may fall from the tree in your front yard, but there are still several leaves attached to the tree’s branches. 
• Or, a chef may have several knives in his kitchen, but he has one particular knife that he prefers to use most often. 
• Unfortunately, there are some exceptions to this rule. For example, the plural of chief becomes chiefs, not chieves. Remember these exceptions so that they do not trip you up in your writing. 

Tip #3. If the noun ends in -um or -on, change the ending to -a to make an irregular plural noun

• For example, there is a difference between witnessing one natural phenomenon and several natural phenomena. 
• In the picture below, a town is being hit simultaneously by both a tornado and a bolt of lightning, or two natural phenomena. 

• Also, did you know that bacteria actually refers to a collection of individual bacterium?
• Or that a collection of information is called data while one piece of information is called a datum? 
• These are both examples of irregular nouns with unusual plural forms. 

Tip #4. Some nouns change vowels when they become irregular plural nouns

• For example, the names of several animals change vowels in their plural form, such as mouse/mice or goose/geese. 
• Likewise, one man joined by another becomes two men, while one woman becomes two women in the plural form. 

Tip #5. Some nouns do not change at all when they become irregular plural nouns

• Nouns like rice, deer, sheep, or moose look exactly the same whether they are in their singular or plural form. Therefore, writers have to use other context clues in their sentences to communicate which form is being used. 
• For example: Suzanne had her name written on a grain of rice at last week’s fair. 
  • We are able to figure out that the singular form of rice is being used in this sentence because the singular form of the regular noun, grain, gives us that clue. 

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Applying the Basics: Irregular Plural Noun Review & Practice

Now that you understand what makes certain plural nouns irregular, let’s practice using them in sentences. 

The Ultimate List of Irregular Plural Nouns 

Refer to the anchor chart below for an extensive list of example irregular plural nouns:

This list, obviously, does not include all irregular plural nouns, and there are some exceptions to these rules; however, it is meant to be used as a guide while identifying these types of nouns.

Irregular Plural Noun Exercises and Review 

Now that you know some common irregular plural nouns, test your ability to accurately identify these nouns.

Select the irregular plural noun(s) in the sentences below. Remember, these nouns will look very different from regular nouns when in their plural form.

1. Aladdin was suddenly surrounded by forty men and his father, the King of Thieves.

• In this sentence, men and thieves are both examples of irregular plural nouns. The singular noun man became men, and the singular noun thief became thieves.

2. The gaggle of geese waddled slowly across the busy intersection, annoying several people who were waiting in their cars.

• In this sentence, geese and people are irregular plural nouns. The singular noun goose changed to geese in its plural form, and the singular noun person became people to show that several individuals were upset. 

3. The town was experiencing multiple crises at once after being hit by three natural phenomena in a row: first a hail storm, then a tornado, and finally, a flood.

• In this sentence, crises and phenomena are both examples of irregular plural nouns. The singular crisis is changed to crises to show the number of problems that faced the town, and the singular phenomenon is changed to phenomena since several natural events happened in succession.

4. While visiting the Rocky Mountains, tourists are likely to see herds of bighorn sheep, moose, and deer.

• In this sentence, sheep, moose, and deer are examples of irregular nouns because these nouns keep the same form whether they are singular or plural. The context clue, herds, indicates to the reader that the plural form of these nouns is being used. 

5. Cacti and fungi thrive in totally opposite environments; while cacti grow best in hot and dry climates, fungi need moisture and darkness to grow. 

• In this sentence, cacti and fungi are examples of irregular plural nouns. These are examples of nouns that end in -us and need to be replaced with an -i to change the noun to plural. 

Pro tip: When evaluating whether a noun is irregular, look at the ending of the word. Is it plural, but it doesn’t have a typical -s or -es ending? If the answer is yes to both of these questions, then your noun is irregular. 

For additional practice, check out Irregular Plural Nouns content on Albert.

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Try for Yourself: Irregular Plural Nouns Quiz

Feeling confident in your understanding of irregular plural nouns? 

Take this short six-question quiz to see what you’ve learned:

1. Does a regular or irregular noun end in -s or -es when changing the noun from singular to plural?

• Answer: Regular 
• Correct Explanation: That’s right! A regular noun only needs an -s or –es ending added to it to make it plural. 
• Incorrect Explanation: Sorry, that’s not right! Remember, a regular plural noun can only have an -s or -es ending while an irregular plural noun goes through more drastic changes.

2. Can a regular or irregular noun look exactly the same whether it is singular or plural?

• Answer: Irregular 
• Correct Explanation: That’s right! There are some irregular plural nouns that look the same in both forms, such as sheep or deer. 
• Incorrect Explanation: Sorry, that’s not right! Remember, a regular noun must have an -s or an -es added to it to make it plural.

3. In this sentence, are the underlined words regular or irregular plural nouns?

The infection was particularly harmful to women as the bacteria tended to attack female patients’ cells more aggressively than male patients’ cells. 

• Answer: Irregular
• Correct Explanation: That’s right! The nouns women and bacteria are irregular because the plural form of these original nouns has changed the word more significantly than a regular noun would. 
• Incorrect Explanation: Sorry, that’s not right! Remember, an irregular noun is a noun that changes more drastically than a regular noun when changed into its plural form.

4. In this sentence, are the underlined words regular or irregular plural nouns?

I held my breath and shut my eyes as the roller coaster swerved around hairpin turns and shot down steep descents. 

• Answer: Regular
• Correct Explanation: That’s right! The nouns eyes, turns, and descents are all regular nouns because the singular form of each noun only needs an -s or -es ending added to make the noun plural. 
• Incorrect Explanation: Sorry, that’s not right! Remember, a regular noun only needs an -s or -es ending added to make the noun plural.

5. In this sentence, are the underlined words regular or irregular plural nouns?

At a recent reunion, several alumni recalled a time during their undergrad when twenty mice escaped from the science lab, and the students had to spend all night retrieving them. 

• Answer: Irregular
• Correct Explanation: That’s right! The nouns alumni and mice are both irregular because these words cannot be made plural by adding -s or -es to the ending: the singular alumnus changes to alumni while mice keeps the same form whether it is singular or plural. 
• Incorrect Explanation: Sorry, that’s not right! Remember, an irregular noun is a noun that changes more drastically than a regular noun when changed into its plural form.

6. In this sentence, are the underlined words regular or irregular plural nouns?

He shot basketball with his closest friends for hours, not caring how much time had passed. 

• Answer: Regular 
• Correct Explanation: That’s right! The nouns friends and hours are regular because the singular form of each noun only needs an -s or -es ending added to make the noun plural.  
• Incorrect Explanation: Sorry, that’s not right!  Remember, a regular noun only needs an -s or -es ending added to make the noun plural. 

For additional practice with irregular plural nouns, check out our practice on Albert: Irregular Plural Nouns.

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Teacher’s Corner for Irregular Nouns

The Common Core English Language Progressive Skills Chart shows that understanding the difference between regular and irregular plural nouns is a skill that should be learned early on and practiced regularly throughout a student’s educational experience. 

For specific standards addressing student comprehension of regular and irregular plural nouns, check out the Common Core State Standards site.

Albert’s irregular noun practice will help keep students from forgetting what they have learned about these nouns, and teachers can rely on our pre-made assessments to gauge student understanding of a wide variety of grammatical concepts throughout the school year. If teachers prefer to assess students on only certain concepts, like irregular nouns and action verbs, teachers are able to create their own assessments using our provided questions.

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Summary on Irregular Nouns

Regular nouns become plural by the writer adding -s or -es to the ending of the noun. 

Irregular plural nouns do not follow the same rules as regular nouns when becoming plural. While there are many kinds of irregular plural nouns, many of these nouns can be categorized based on their similarities to other irregular plural nouns. 

Be sure to check out our grammar course for more irregular plural noun practice. 

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