Compound Nouns

A compound noun is a noun made up of two or more words that work together to name a single person, place, thing, or idea. For example, "toothbrush" is made from "tooth" + "brush." Compound nouns can be written as one word, two separate words, or joined with a hyphen.

What You'll Learn

How to identify compound nouns in sentences
The three forms of compound nouns: closed, open, and hyphenated
How to choose the correct form when writing compound nouns
Common compound nouns you will encounter in everyday life and in exams

When to Use

Naming everyday objects: "Please put your toothbrush back in the cup after brushing your teeth."
Describing places: "The students lined up outside the classroom before the lesson started."
Talking about nature and weather: "Heavy rainfall caused flooding along the road near the hawker centre."
Referring to people by their role: "The bus driver waited for the last passenger to board."
Describing activities or events: "We watched the beautiful fireworks at the National Day celebration."

How to Form

The Three Forms of Compound Nouns

Compound nouns are formed by combining two or more words. They come in three forms:

Form	How It Looks	Examples
Closed	One word, no spaces	toothbrush, classroom, rainfall, football
Open	Two separate words	bus stop, ice cream, swimming pool, post office
Hyphenated	Words joined by a hyphen	mother-in-law, merry-go-round, passer-by

Common Word Combinations That Form Compound Nouns

Pattern	Examples
noun + noun	toothbrush, classroom, football, raincoat, sunlight
adjective + noun	blackboard, greenhouse, highway, software
verb + noun	swimsuit, washing machine, driving licence
noun + verb	rainfall, sunrise, haircut, nosebleed
preposition + noun	underground, overcoat, upstairs, output
verb + preposition	check-up, breakdown, take-off, warm-up

How to Tell If Two Words Form a Compound Noun

Ask yourself: do the two words together name one thing that is different from what each word means on its own?

Separate Words	Compound Noun	Why It Is a Compound Noun
black + board	blackboard	Not just any black board -- it is a writing surface
green + house	greenhouse	Not just a green house -- it is a glass building for plants
sun + flower	sunflower	Not a flower made of sun -- it is a specific plant
fire + fighter	firefighter	Not a fighter on fire -- it is a person who puts out fires

Key Rules

A compound noun names one thing: Even though it is made from two or more words, a compound noun refers to a single person, place, thing, or idea. "Toothbrush" is one object, not a tooth and a brush separately.
The last word usually tells you what kind of thing it is: In "raincoat," the main idea is "coat." In "sunflower," the main idea is "flower." The first word describes or narrows the meaning.
The form must be memorised: There is no single rule that tells you whether a compound noun is closed, open, or hyphenated. "Toothbrush" is one word, but "bus stop" is two words. You need to learn the correct form for each one.
Plurals are formed on the main noun: For most compound nouns, add -s to the end: "toothbrushes," "classrooms," "bus stops." For hyphenated compounds where the main noun comes first, add -s to that noun: "mothers-in-law" (not "mother-in-laws"), "passers-by" (not "passer-bys").
Do not confuse compound nouns with adjective + noun pairs: A compound noun has a special, fixed meaning. "A hot dog" (temperature) is adjective + noun, but "a hotdog" is a compound noun naming a type of food.
Use a dictionary when unsure: If you are not sure whether a compound noun is closed, open, or hyphenated, check a dictionary. Over time, many open and hyphenated forms become closed (e.g., "e-mail" has become "email").

Common Mistakes

Wrong	Right	Why
I left my tooth brush on the sink.	I left my toothbrush on the sink.	"Toothbrush" is a closed compound noun -- one word, no space.
The class room was very noisy.	The classroom was very noisy.	"Classroom" is a closed compound noun -- one word, no space.
We waited at the busstop for ten minutes.	We waited at the bus stop for ten minutes.	"Bus stop" is an open compound noun -- two separate words.
My mother-in-laws are coming for dinner.	My mothers-in-law are coming for dinner.	The main noun is "mothers," so the plural -s goes on "mother."
She bought a new swim suit for the competition.	She bought a new swimsuit for the competition.	"Swimsuit" is a closed compound noun -- one word, no space.
There was a lot of rain fall yesterday.	There was a lot of rainfall yesterday.	"Rainfall" is a closed compound noun -- one word, no space.

Clue Words

Words that often form closed compound nouns:

tooth-, rain-, sun-, class-, foot-, bed-, book-, day-, fire-, news-, home-

Words that often form open compound nouns:

bus stop, ice cream, swimming pool, post office, living room, high school, full moon

Words that often form hyphenated compound nouns:

mother-in-law, merry-go-round, check-up, passer-by, well-being, six-year-old

Tip: If two words together name one special thing and you always see them used together, they are probably a compound noun. Read widely and pay attention to how these words are written -- over time, you will remember the correct form naturally.

Practice Tips

The "one thing" test: When you see two words together, ask: "Do these words name one single thing?" If yes, they are likely a compound noun. A "bus stop" is one place, not a bus and a stop.
Spot the main word: Look at the last word of the compound noun -- it tells you the category. In "sunflower," it is a type of flower. In "goalkeeper," it is a type of keeper. This helps you understand the meaning and remember the word.
Group by form: When revising, sort compound nouns into three lists -- closed, open, and hyphenated. This helps you remember which form each one takes.
Check plurals carefully: Before adding -s, find the main noun. For most compounds, add -s at the end. For hyphenated compounds with the main noun first, add -s to that noun: "passers-by," "mothers-in-law."

Quick Reference

Form	How to Write	Common Examples	Plural Rule
Closed	One word	toothbrush, classroom, rainfall, football, sunflower	Add -s at the end: toothbrushes
Open	Two separate words	bus stop, ice cream, swimming pool, post office, living room	Add -s to the last word: bus stops
Hyphenated	Joined by a hyphen	mother-in-law, merry-go-round, passer-by, check-up	Add -s to the main noun: mothers-in-law

Quick Identification Guide

Question	If Yes
Do the two words together name one specific thing?	It is likely a compound noun
Does the meaning change from the individual words?	It is likely a compound noun
Are the two words always used together in this order?	It is likely a compound noun

Compound Nouns (P4) (Primary 4)