Compound nouns become one word, remain as two words or are hyphenated
We often invent new words by combining existing words to form what is known as a compound noun.
Here are some of the ways we create compound nouns.
Verb plus adverb, or preposition and adverb, or preposition plus verb
When the word order is verb plus adverb, you usually need a hyphen.
look-out, make-up, go-ahead
Some hyphens drop out with constant use (lookout is now common).
When the word order is adverb plus verb, we usually write the compound noun as one word.
downpour, bypass, output
Verb plus noun, and noun plus verb
Most verb-plus-noun and noun-plus-verb compound words are usually one word (scarecrow), though a few are hyphenated (sun-dry).
Noun plus noun
Opinion differs on whether to hyphenate noun-plus-noun compound words, but they are usually hyphenated if both parts are of equal status.
Adjective plus noun
Adjective-plus-noun compound words are usually written as two words.
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