Home / English / Word Study / Compound Words: Two Words Join to Make a New One
Word Study · Compound words
Compound Words: Two Words Join to Make a New One
Split and build compound words like snowball and sunflower, learn when to write them as one word, two words or with a hyphen, and spot ones that trick you.
The idea
A compound word is made by joining two whole words to make a new word: snow + ball = snowball, back + pack = backpack. In earlier lessons you added prefixes such as un- and suffixes such as -ful. A prefix or suffix cannot stand alone, but each part of a compound is a real word.
Most of the time the parts help with the meaning. The second word usually names the thing, and the first word tells what kind: a bookshelf is a shelf for books, a toothbrush is a brush for teeth, and a firefighter is someone who fights fires.
Compounds are written in three ways. Closed compounds are one word: sunflower, playground, homework. Open compounds keep a space: ice cream, hot dog, bus stop. Hyphenated compounds use a short dash called a hyphen: twenty-one, well-known. Two rules are dependable at this level: numbers from twenty-one to ninety-nine always get a hyphen, and describing words such as well-known usually take a hyphen before a noun (a well-known song). For other words, check a dictionary, because the way a compound is written can change over time.
Watch for compounds that trick you. A butterfly is not made of butter, and a hot dog is not a warm dog. Breakfast makes sense once you know that fast can mean a time without food. Sometimes the sound changes too: in cupboard the p is silent.
Finally, a word is not a compound just because you can find small words inside it. Carpet contains car and pet, and button contains but, but their meanings do not come from those parts. Ask: do these two words build the meaning of the new word?
Word bank
snowball
noun · SNOH-bawlsnow + ball; a ball of packed snow
Example: We built a fort and made a pile of snowballs.
sunflower
noun · SUN-flow-ersun + flower; a tall flower with a big yellow head that faces the sun when young
Example: The sunflower in our garden grew taller than Dad.
backpack
noun · BAK-pakback + pack; a bag you carry on your back
Example: Put your lunch in your backpack.
toothbrush
noun · TOOTH-brushtooth + brush; a small brush for cleaning teeth
Example: Get a new toothbrush every few months.
bookshelf
noun · BUK-shelfbook + shelf; a shelf for holding books
Example: The atlas is on the bottom bookshelf.
playground
noun · PLAY-growndplay + ground; an outdoor area with equipment for children to play on
Example: The playground has two slides and a climbing wall.
sidewalk
noun · SYD-wawkside + walk; a paved path beside a street for people walking
Example: Walk on the sidewalk, not on the road.
firefighter
noun · FYR-fy-terfire + fighter; a person whose job is to put out fires and help in emergencies
Example: A firefighter visited our class during Fire Prevention Week.
homework
noun · HOHM-werkhome + work; schoolwork you do at home
Example: I finished my homework before dinner.
cupboard
noun · KUB-erdcup + board; a cabinet with shelves and a door. The p is silent, so the parts do not sound the same as alone.
Example: The plates are in the cupboard above the sink.
breakfast
noun · BREK-fustbreak + fast; the first meal of the day. Here fast means a time of not eating, so breakfast "breaks" the night's fast.
Example: We had oatmeal for breakfast.
butterfly
noun · BUT-er-flybutter + fly; an insect with large colourful wings. The meaning does not come from butter or from a fly.
Example: A butterfly landed on the milkweed.
hot dog
noun · HOT dawgan open compound: a sausage in a long bun. It is not a warm dog!
Example: We bought hot dogs at the game.
ice cream
noun · YS kreeman open compound: a frozen sweet food made from milk or cream
Example: Can I have ice cream for dessert?
bus stop
noun · BUS stopan open compound: a place where a bus stops to let people on and off
Example: Wait for the school bus at the bus stop.
twenty-one
number · TWEN-tee-WUNa hyphenated compound: numbers from twenty-one to ninety-nine are joined with a hyphen when written in words
Example: There are twenty-one students in our class.
well-known
adjective · wel-NOHNa hyphenated compound: famous; known by many people. Use the hyphen before a noun: a well-known song.
Example: "O Canada" is a well-known song.
rainbow
noun · RAYN-bohrain + bow; an arc of colours in the sky when sunlight shines through raindrops. Bow here means a curved shape.
Example: A rainbow appeared after the storm.
Worked examples
Example 1 · Split and explain
What does playground mean?
- Split it: play + ground.
- The second word names the thing: a piece of ground.
- The first word tells what kind: ground for playing.
A playground is an area of ground where children play.
Example 2 · One word, two words or a hyphen?
Write 57 in words.
- 57 is between twenty-one and ninety-nine.
- Numbers in that range are joined with a hyphen.
- fifty + seven → fifty-seven.
fifty-seven
Example 3 · When the parts do not add up
Is a butterfly a fly made of butter?
- Split it: butter + fly.
- Check the meaning: a butterfly is an insect with large wings.
- Neither part explains the meaning, so remember this compound as a whole word.
No. Butterfly is a compound whose meaning does not come straight from its parts.
Example 4 · Is it really a compound?
Is carpet a compound word?
- Look for two whole words: car + pet.
- Ask whether they build the meaning. A carpet is a floor covering; it has nothing to do with cars or pets.
- The small words are only hidden letters.
No. Carpet is not a compound word.
Example 5 · Build a word family
Build compound words that start with rain.
- Think of whole words that join after rain.
- rain + bow, rain + coat, rain + drop, rain + storm.
- Check each meaning: a raincoat is a coat for rain.
rainbow, raincoat, raindrop, rainstorm
Common mistakes
Why this fails: -ful is a suffix, not a whole word. Both parts of a compound must be words on their own: care + ful does not count, but cup + board does.
Why this fails: A compound joins two words that build its meaning. Car and pet do not explain carpet.
Why this fails: In most Canadian dictionaries these are written as two words: ice cream, hot dog. Check a dictionary when you are not sure.
Why this fails: Numbers from twenty-one to ninety-nine are written with a hyphen.
Why this fails: Some compounds do not add up, such as butterfly and hot dog. Use the parts as a first clue, then check that the meaning fits the sentence.
Foundation
Foundation practice
Split compound words and join two words to make one.
1. Split sunflower into its two smaller words.
2. Join tooth and brush to make a compound word.
3. Which word joins with ball to make a compound word you can throw in winter?
4. Which word is a compound word?
- careful
- backpack
- running
- unhappy
5. Use the two parts to explain what a bookshelf is.
Practice
Practice practice
Decide how a compound is written and whether its parts explain it.
6. Which compound word is usually written as two separate words?
- playground
- sidewalk
- ice cream
- homework
7. How should you write the number 34 in words?
- thirtyfour
- thirty four
- thirty-four
- thirty-and-four
8. Which compound word's meaning does NOT come straight from its two parts?
- butterfly
- toothbrush
- bookshelf
- snowball
9. Carpet contains the letters car and pet. Is carpet a compound word?
- Yes, a car for pets
- No: car and pet do not give carpet its meaning
- Yes, because it has two small words inside
- No, because compound words always have a hyphen
10. Fix the spelling: "We ate hotdogs and icecream at the fair."
11. Which compound word has a letter that goes silent when the two words join?
- cupboard
- sunflower
- rainbow
- sidewalk
Think
Think practice
Explain the rule, not just the answer.
12. Why is breakfast a compound word, even though it is not a fast meal?
13. Which sentence uses the compound word correctly?
- She is a well known author.
- She is a wellknown author.
- She is a well-knowned author.
- She is a well-known author.
14. Which group contains only closed compound words?
- bus stop, hot dog, ice cream
- twenty-one, well-known, sidewalk
- careful, unhappy, backpack
- sunflower, rainbow, homework
15. Make two new compound words that start with snow, and use one in a sentence.
Answer key
- 1. sun + flower
Each part is a real word on its own: sun and flower. - 2. toothbrush
A toothbrush is a brush for your teeth. Closed compounds are written as one word with no space. - 3. snowball
Snow + ball = snowball, a ball made of packed snow. - 4. backpack
Backpack is two whole words, back + pack. Careful is care + the suffix -ful, running is run + -ing, and unhappy is the prefix un- + happy. A prefix or suffix is not a whole word, so those are not compounds. - 5. A shelf for books.
In many compounds, the second word names the thing and the first word tells what kind: a shelf for books. - 6. ice cream
Ice cream is an open compound, written with a space. Playground, sidewalk and homework are closed compounds, written as one word. - 7. thirty-four
Numbers from twenty-one to ninety-nine are written with a hyphen: thirty-four. Thirtyfour runs the words together, thirty four leaves out the hyphen, and thirty-and-four adds a word that is not used. - 8. butterfly
A butterfly is not made of butter and is not a fly. The other three mean exactly what their parts say: a brush for teeth, a shelf for books and a ball of snow. - 9. No: car and pet do not give carpet its meaning
Finding small words hidden in a word does not make it a compound. A compound joins two words whose meanings build the new word. Most compounds have no hyphen, so that reason is wrong too. - 10. We ate hot dogs and ice cream at the fair.
Hot dog and ice cream are open compounds in most Canadian dictionaries, so they keep a space. Some brands and older books write hotdog, so check a dictionary when unsure. - 11. cupboard
Cupboard is said KUB-erd: the p is silent and board sounds like erd. In sunflower, rainbow and sidewalk each part still sounds like the word on its own. - 12. Breakfast is break + fast. Here fast means a time of not eating, like the night while you sleep. Breakfast is the meal that "breaks" that fast.
Some compounds use an older meaning of a word. Looking up the parts can explain the whole. - 13. She is a well-known author.
Before a noun (author), well-known takes a hyphen. Leaving out the hyphen or joining the words are common slips, and knowned is not a word. - 14. sunflower, rainbow, homework
Sunflower, rainbow and homework are each one word with no space or hyphen. Bus stop, hot dog and ice cream are open; twenty-one and well-known are hyphenated; careful and unhappy have a suffix or prefix, not two words. - 15. Examples: snowflake, snowman, snowstorm, snowplow, snowsuit. The snowplow cleared our street at 6 a.m.
Each answer should join snow with another whole word, written as one word, and the sentence should use the meaning correctly.