Compound Nouns
Learn how two or more words can combine to name one single person, place or thing, and how those words are written.
Two words, one noun
A compound noun is made of two or more words joined to name one thing.
A compound noun combines two or more words to create a single noun with its own meaning. Tooth and brush combine to form toothbrush, a single object used to clean teeth.
The combined meaning of a compound noun is often different from simply adding the meanings of the separate words together.
Compound nouns can be written as one word, as two words joined by a hyphen, or as two separate words.
Before you begin
Compound nouns are still nouns.
This lesson looks at how words combine to form a noun. It does not change what a noun is or how it functions in a sentence.
If you would like to review what nouns are and how they work, begin with the Nouns lesson.
The central idea
A compound noun names one thing, even when it is written as two words.
Compare a compound noun with two separate, unrelated nouns.
01
Two Separate Nouns
Two nouns placed together without combining into one meaning simply describe two different things.
a table and a lamp
a book and a pen
02
A Compound Noun
A compound noun combines two words into one noun with its own specific meaning.
tablecloth
notebook
The useful question is: Do the two words name one single thing together?
fire + fighter → firefighter
swimming + pool → swimming pool
mother + in-law → mother-in-law
If the two or more words work together to name one specific person, place or thing, they form a compound noun.
Three written forms
Compound nouns are written as one word, a hyphenated word, or two separate words.
Closed compound nouns
toothbrush
notebook
classroom
She packed her toothbrush before the trip.
Closed compound nouns are written as a single word with no space or hyphen.
Hyphenated compound nouns
mother-in-law
editor-in-chief
runner-up
My mother-in-law is visiting next week.
Hyphenated compound nouns join their words with one or more hyphens.
Open compound nouns
swimming pool
bus stop
coffee table
We waited at the bus stop for ten minutes.
Open compound nouns are written as two separate words, but they still name one single thing.
The written form is not always predictable
There is no single rule that decides whether a compound noun is closed, hyphenated or open. The same idea can even be written differently over time, such as e-mail becoming email. When in doubt, a dictionary shows the accepted form.
How compound nouns are built
Compound nouns combine different word types.
Noun + noun
doorbell
football
rainbow
Adjective + noun
greenhouse
blackboard
software
Verb + noun
washing machine
driving licence
swimming pool
Noun + verb or particle
sunrise
breakdown
check-in
Different combinations of word types produce compound nouns, but the result always functions as a single noun in a sentence.
A closer look
A compound noun can mean something different from its separate words.
Comparing a compound noun with the same words used separately shows how much the combination changes the meaning.
01
Greenhouse
A greenhouse is a glass building used for growing plants. It does not need to be green at all.
02
A green house
A green house is simply a house that happens to be painted green. Here, green and house are two separate words, not a compound noun.
03
Blackboard
A blackboard names a specific classroom surface used for writing, whether or not it is actually black.
04
A black board
A black board simply describes any board that is black in colour.
Plurals of compound nouns
The plural ending usually attaches to the main word.
This pattern is covered in more depth in the Singular and Plural Nouns lesson, but it is worth reviewing here for compound nouns specifically.
Plural added to the main word
passer-by → passers-by
mother-in-law → mothers-in-law
runner-up → runners-up
Plural added to the end of a closed compound noun
toothbrush → toothbrushes
classroom → classrooms
When a compound noun is written as one word, the plural ending is added at the end, following the usual spelling rules.
A useful decision guide
Ask what the combined words name, then check the written form.
01
Do the two words together name one specific thing?
If so, they likely form a compound noun.
bus stop
toothbrush
02
Is it written as one word, a hyphenated word, or two words?
Check a dictionary, since the written form is not always predictable.
03
Does the plural ending belong on the main word?
Hyphenated and open compound nouns usually pluralise the main word.
runners-up
04
Does the meaning change from the separate words?
A true compound noun, such as greenhouse, often names something more specific than its separate words would suggest.
Common mistakes
Do not assume every compound noun follows the same spelling pattern.
The written form must be checked, not guessed.
bus stop → two words
classroom → one word
editor-in-chief → hyphenated
Similar compound nouns can be written in different ways, so the spelling should be checked rather than assumed from a pattern.
Adding -s to the wrong word in a hyphenated compound noun.
Not: mother-in-laws
Correct: mothers-in-law
The plural ending usually belongs on the main word, not on the final word.
Confusing a compound noun with two separate describing words.
greenhouse → one specific thing
a green house → any house that is green
The meaning, not just the spelling, shows whether the words have combined into a compound noun.
Check your understanding
Compound noun or two separate words?
Choose the correct description for the highlighted phrase.
She waited at the bus stop in the rain.
✅ Exactly! Bus stop names one specific place, even though it is two words.
❎ Not quite. Ask whether the two words together name one specific thing.
Open compound nouns are still written as two separate words.
He painted the fence with a bright red colour.
✅ Exactly! Bright red describes the colour but does not name one combined thing.
❎ Not quite. Check whether the words combine into one specific noun.
Please put the milk back in the fridge, next to the toothbrush holder.
✅ Exactly! Toothbrush combines tooth and brush into one closed compound noun.
❎ Not quite. Look at the single word toothbrush.
My mother-in-law called this morning.
✅ Exactly! Mother-in-law is a hyphenated compound noun naming one specific person.
❎ Not quite. The hyphens join the words into a single noun.
Choose the best explanation
Select the sentence that explains the compound noun correctly.
Why is greenhouse a compound noun rather than two separate words?
✅ Exactly! The combined word names a specific structure, separate from its literal colour.
❎ Not quite. Think about what the word names, rather than how it is spelled or coloured.
Why does passers-by add the plural ending to passer instead of by?
✅ Exactly! The plural ending attaches to the main word in a hyphenated compound noun.
❎ Not quite. Identify which word names the person or thing at the centre of the phrase.
Which pair contains one closed compound noun and one open compound noun?
✅ Exactly! Notebook is written as one word, while swimming pool is written as two.
❎ Not quite. Look for one noun written as a single word and one written with a space.
Try it another way
Combine the two words into a compound noun.
Type the compound noun that completes each sentence.
✅ Exactly! Tooth and brush combine into the closed compound noun toothbrush.
❎ Not quite. Join the two words together with no space.
✅ Exactly! Bus stop is an open compound noun, written as two separate words.
❎ Not quite. Keep bus and stop as two separate words.
✅ Exactly! Runner-up joins the two words with a hyphen.
❎ Not quite. Join runner and up with a hyphen.
Edit the sentence
Rewrite each sentence using the correct compound noun.
Use the note in brackets to complete the rewrite.
The person who fights fires arrived within minutes. (firefighter)
✅ Exactly! Firefighter replaces the longer phrase with a single compound noun.
❎ Not quite. Replace the longer phrase with the single word firefighter.
The machine used for washing broke down again. (washing machine)
✅ Exactly! Washing machine is an open compound noun written as two words.
❎ Not quite. Use washing machine as two separate words.
Two people holding the position of editor-in-chief reviewed the article. (editors-in-chief)
✅ Exactly! The plural ending attaches to the main word, editor.
❎ Not quite. Add the plural ending to editor, not to chief.
Quick review
Two or more words, one specific meaning.
Compound nouns combine two or more words to name one specific person, place or thing.
They can be written as one word (toothbrush), a hyphenated word (mother-in-law), or two separate words (bus stop).
There is no single spelling rule, so an unfamiliar compound noun should be checked in a dictionary.
Compound nouns can combine different word types, including noun + noun, adjective + noun and verb + noun.
A compound noun often has a specific meaning that is different from its separate words, as in greenhouse versus a green house.
The plural ending usually attaches to the main word in hyphenated and open compound nouns, as in passers-by.
Remember
Ask what the combined words name.
If two or more words work together to name one specific person, place or thing, they form a compound noun, regardless of whether they are written as one word, a hyphenated word or two separate words.