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Grammar A1 Plural Rules & Exceptions

Compound noun plurals

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Compound noun plurals

What is a Compound Noun?

A compound noun is two or more words that together make one noun. For example, 'toothbrush' is a compound noun. It is one thing made from two words: 'tooth' + 'brush'. Other examples are 'football', 'classroom', and 'mother-in-law'. When you want to talk about more than one, you need to make it plural.

How to Make Compound Nouns Plural

Most compound nouns are made plural like normal nouns. You usually add -s or -es to the end: 'toothbrush' becomes 'toothbrushes'. However, when a compound noun has two words joined with a hyphen (like 'mother-in-law'), you make the most important word plural: 'mothers-in-law'. The important word is usually at the beginning.

Special Cases

Some compound nouns are irregular and do not follow the normal rules. For example, 'man' + 'woman' in compounds: 'policeman' becomes 'policemen', not 'policemans'. The word 'man' or 'woman' inside changes to 'men' or 'women'. This is important to remember for words like 'fireman', 'businessman', and 'saleswoman'.

Compound Noun Plurals at a Glance

Type Plural Rule Singular → Plural Note
One word Add -s or -es to the end of the whole word toothbrush → toothbrushes Treat it like any regular noun; the last letter determines -s vs. -es
Hyphenated Pluralise the most important (head) noun, usually the first one mother-in-law → mothers-in-law The head noun carries the meaning; words like in and of are never pluralised
Two separate words Pluralise the head (main) noun, which is usually the first word post office → post offices The second word acts as a modifier; only the noun being counted changes
Formula
Formula
Compound noun (written together) + + s or -es
toothbrush → toothbrushes

Examples

I have two toothbrushes in my bathroom.
I have two toothbrushes in my bathroom.
Written compound · Regular plural
There are many classrooms in our school.
There are many classrooms in our school.
Written compound · Regular plural
My mothers-in-law are very nice.
My mothers-in-law are very nice.
Hyphenated compound · Important word plural
The policemen are here to help.
The policemen are here to help.
Irregular compound · 'Man' changes to 'men'
We need new football balls for the team.
We need new football balls for the team.
Written compound · Regular plural
The businessmen have a meeting tomorrow.
The businessmen have a meeting tomorrow.
Irregular compound · 'Man' changes to 'men'
When to use it
Home and Family
Talk about items in your home and family members with hyphenated relationships.
"I need to buy new toothbrushes and my sisters-in-law are coming to visit."
School and Work
Describe people and places at school or in a job using compound nouns.
"The businessmen and saleswomen work in three office buildings."
Sports and Games
Name sports equipment and activities that use compound nouns.
"We need new footballs and basketballs for the teams."
Signal words
compound noun hyphenated written together plural man/men woman/women more than one
Common Mistakes
✕
Wrong
I have three toothbrush in my bathroom.
✓
Correct
I have three toothbrushes in my bathroom.
Compound nouns need -s or -es to be plural, just like regular nouns.
✕
Wrong
My mother-in-laws are visiting next week.
✓
Correct
My mothers-in-law are visiting next week.
In hyphenated compounds, make the first (most important) word plural, not the last word.
✕
Wrong
The policemans stopped the car.
✓
Correct
The policemen stopped the car.
When 'man' or 'woman' is part of a compound, change it to 'men' or 'women', not add -s.
✕
Wrong
There are five classroomes in this building.
✓
Correct
There are five classrooms in this building.
Add -s, not -es, to 'classroom' because it ends in a consonant + m, not 's', 'x', 'z', 'ch', or 'sh'.
KEY TAKEAWAYS

What to Remember

  • A compound noun is two or more words that together make one noun.
  • Most compound nouns add -s or -es to the end to become plural.
  • For hyphenated compound nouns, add -s or -es to the most important word.
  • 'Toothbrush' becomes 'toothbrushes' and 'mother-in-law' becomes 'mothers-in-law' following these plural rules.
  • Always check if the compound noun is written as one word or hyphenated.
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Foreign word plurals (data, criteria, phenomena)