Compound Words
What Are Compound Words?
A compound word is formed when two or more words are joined together to create a new word with its own meaning. The combined meaning is often different from — or more specific than — the individual words. English has thousands of compound words, and learning their patterns makes your spelling and writing far more accurate.
Key Terms
| Term | Definition | Example |
|---|---|---|
| Closed compound | Two words written as one | sunflower, bedroom |
| Open compound | Two words written with a space | ice cream, high school |
| Hyphenated compound | Two words joined with a hyphen | well-known, up-to-date |
| Compound noun | A compound word functioning as a noun | toothbrush, car park |
| Compound adjective | A compound word functioning as an adjective | fast-paced, soft-spoken |
Three Types of Compound Words
1. Closed Compounds (One Word)
The two words are merged into a single word with no space or hyphen.
Examples:
- sun + flower = sunflower
- tooth + brush = toothbrush
- foot + ball = football
- note + book = notebook
- basket + ball = basketball
- bed + room = bedroom
2. Open Compounds (Two Words)
The two words are written separately but function together as one unit of meaning.
Examples:
- ice cream
- high school
- post office
- full moon
- living room
- coffee table
3. Hyphenated Compounds
The words are joined with a hyphen. This is most common with compound adjectives placed before a noun.
Examples:
- well-known author
- up-to-date information
- self-made millionaire
- state-of-the-art technology
- two-year-old child
Key rule: Compound adjectives are usually hyphenated before the noun but not after a linking verb.
- She is a well-known scientist. (before noun — hyphen)
- The scientist is well known. (after verb — no hyphen)
How Compound Words Develop Over Time
Compound words often follow a pattern of evolution:
- Start as two separate words (web site)
- Become hyphenated (web-site)
- Finally become one closed word (website)
This is why you may see different spellings in different sources — language is always changing.
Worked Examples
Identify the type:
| Compound Word | Type |
|---|---|
| sunlight | closed |
| fire station | open |
| mother-in-law | hyphenated |
| headache | closed |
| swimming pool | open |
| long-term | hyphenated |
Using compound adjectives correctly:
- It was a fast-paced thriller. (hyphen — before noun)
- The thriller was fast paced. (no hyphen — after verb)
Common Mistakes
- Hyphenating all compound words: Not every compound needs a hyphen. "Sun-flower" and "foot-ball" are incorrect — these are closed compounds.
- Missing hyphens in compound adjectives before nouns: "a well known actor" should be "a well-known actor."
- Adding hyphens after linking verbs: "She is well-known" — no hyphen needed here.
- Confusing compound words with prefixed words: "unhappy" is a prefixed word, not a compound; "sunflower" is a compound.
Tips and Tricks
- When unsure, check a dictionary — it will tell you whether a compound is open, closed, or hyphenated.
- Compound adjectives before nouns almost always need a hyphen: "a five-year plan", "a ten-minute walk".
- Notice compounds in your reading — you will quickly build a natural sense for which words merge together.
- Many nouns for places are open compounds: car park, bus stop, town hall, sports centre.
- Phrasal verbs can become compound nouns: "to break down" → a "breakdown"; "to log in" → a "login".
Quick Reference
| Type | Format | Examples |
|---|---|---|
| Closed | One word | sunflower, notebook, football, bedroom |
| Open | Two words | ice cream, high school, post office |
| Hyphenated | Hyphen between | well-known, up-to-date, self-made |
| Compound adjective before noun | Hyphenated | a fast-paced race, a two-year plan |
| Compound adjective after verb | No hyphen | the race was fast paced |