- Grammar rules with examples.
A compound noun is a noun that is formed from two or more unique words and has a more specific meaning than the separate words. The compound word can be written as separate words (mother tongue), as a single word (grandmother) or with hyphens (mother-in-law).
- Open compound nouns (swimming pool, first aid, hot dog)
- Closed compound nouns (grandmother, snowball, railway)
- Hyphenated compound nouns (mother-in-law, merry-go-round)
The open compound noun is made up of two words that are written as separate words but their combination creates a new, single meaning.
air force, fairy tale, street lamp, goose bumps
The closed compound noun combines two words that are written as one word with a new meaning.
banknote, honeymoon, painkiller, password, rainbow, runway
The hyphenated compound noun is a combination of two or more words that are connected with hyphens. They are less common in modern English than in the past.
co-worker, passer-by, runner-up, word-of-mouth
There are no clear rules how to form a compound noun in English. With the relaxed attitude toward spelling, a lot of compound nouns gradually develop. A good dictionary will help you to find out how to write a compound word.
all right | alright
back yard | back-yard | backyard
check in | check-in
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English nouns Countable and uncountable nouns, singular and plural nouns, proper nouns and group nouns.