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

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:

1. Start as two separate words (web site)
2. Become hyphenated (web-site)
3. 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:

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