The rules for when a hyphen is used can be a bit confusing because there’s just not a ton of agreement on it and it’s changing all the time. The best advice is to keep a dictionary handy and try looking up the word first. If you can’t find the compound word in the dictionary, treat it as two separate words.
Put simply, hyphens are used to join two words into a compound word.
Adjectives
When two words are used as a single adjective before a noun and act as a single modifier, they should be hyphenated:
- air-conditioned room
- sugar-coated words
When the two words are used after a noun, they should NOT be hyphenated:
- The room was air conditioned.
- His words were sugar coated.
Adverbs
When adverbs not ending in “ly” are used in front of a noun, they are hyphenated:
- long-anticipated reunion
- much-needed break
Numbers
A hyphen is used with compound numbers between twenty-one and ninety-nine:
- twenty-six
- eighty-three
Hyphenate any spelled-out fractions:
- one-half
- three-quarters
Prefixes
Prefixes are hyphenated when they come before proper nouns:
- un-Canadian
Hyphenate prefixes ending in an “a” or an “i” only when the root word begins with the same letter:
- semi-inherent
- ultra-antagonistic
If the prefix ends with “e” or “o” and the root word begins with the same letter, they are generally not hyphenated:
- coordinate
- preexisting
If prefix is “self” and the word is not “selfish” or “selfless”, it should be hyphenated:
- self-assured
- self-motivated
If the prefix “ex” is used, the word should be hyphenated:
- ex-mayor
- ex-wife
Use a hyphen with the prefix “re” only if “re” means “again” and omission would cause confusion with another word:
- Will she recover her health?
- Will she re-cover the couch?
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