Definition · Plain-language
Hyphen
A hyphen ( - ) is a short punctuation mark used to join words or parts of words, as in compound adjectives (well-known) and spelled-out numbers (twenty-one).
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Joining compound modifiers
The hyphen’s most common job is to join two or more words that work together as a single adjective before a noun. "A well-known author" uses a hyphen because well and known combine to modify author; without it, the reader might pause over "well" on its own. The same applies to phrases like "a five-year-old child", "a state-of-the-art lab" and "a long-term plan". Crucially, the hyphen usually disappears when the same words come after the noun: "the author is well known" needs no hyphen because the words are not bunched before a noun. This before/after distinction is one of the most useful hyphen rules.
Numbers, prefixes and word breaks
Beyond compound modifiers, the hyphen has several settled uses. It joins spelled-out numbers from twenty-one to ninety-nine and fractions used as modifiers (a two-thirds majority). It attaches some prefixes to roots, especially to avoid awkward letter pairs or ambiguity: re-enter, co-operate, ex-husband, anti-inflammatory. It also breaks a long word at the end of a printed line, splitting between syllables. Many compounds that begin hyphenated eventually merge into single words over time — "e-mail" became "email", for instance — so dictionaries are the best guide to whether a given compound is hyphenated, spaced or closed up.
Hyphen versus the dashes
The hyphen is frequently confused with the longer dashes, but they are distinct marks with distinct jobs. The hyphen (-) joins words and is the shortest. The en dash (–), roughly the width of a capital N, marks spans and ranges — pages 20–35, the 1939–45 war — and connections between two things. The em dash (—), the width of a capital M, marks a strong break or parenthetical aside within a sentence. Because a standard keyboard has only a hyphen key, writers often type a hyphen where an en or em dash belongs; word processors usually offer the longer dashes through autocorrect or special characters. Keeping the three straight is a mark of careful punctuation.
Key facts
At a glance
- Definition: a short mark ( - ) joining words or parts of words
- Compound adjectives: well-known author, long-term plan (before a noun)
- Numbers: joins twenty-one to ninety-nine and fraction modifiers
- Prefixes: re-enter, ex-partner, co-operate where clarity needs it
- After the noun: the hyphen often drops (the author is well known)
- Not the same as: the en dash (–, ranges) or em dash (—, breaks)
Common misconceptions
What people often get wrong
Often heard: A hyphen and a dash are the same mark.
Actually: They differ in length and job. The hyphen joins words (well-known); the en dash marks ranges (10–20); the em dash marks sentence breaks (— like this —). They are three separate marks.
Often heard: A compound adjective is always hyphenated, wherever it appears.
Actually: The hyphen usually applies only before the noun. "A well-known result" takes a hyphen, but "the result is well known" does not, because the words no longer bunch before a noun.
Often heard: Every prefix needs a hyphen, as in "pre-view" or "co-worker".
Actually: Most prefixes attach with no hyphen (preview, coworker). Hyphens are used mainly to prevent awkward letter pairs or ambiguity, such as re-enter or re-cover (versus recover); check a dictionary.
Going deeper
