A hyphen denotes two or more words to be read as one but try to cut and join if you can. Check dictionaries.
The hyphen ( ‐ ) is used to join words and to separate syllables of a single word. It is often confused with dashes ( –, —, ― ), which are longer and have different uses.
Hyphens are mostly used to break single words into parts or to join ordinarily separate words into single words. Spaces should not be placed between a hyphen and either of the words it connects except when using a suspended or “hanging” hyphen (e.g. nineteenth- and twentieth-century writers).
A definitive collection of hyphenation rules does not exist but styles prescribe different usage guidelines. The rules of style that apply to dashes and hyphens have evolved to support ease of reading in complex constructions.
The use of the hyphen has been steadily declining. Compounds that might once have been hyphenated are increasingly left with spaces or are combined into one word. The advent of the internet and the increasing prevalence of computer technology have given rise to a subset of common nouns that may in the past have been hyphenated (eg toolbar). yphenation is also routinely used to avoid unsightly spacing in justified texts (for example, in newspaper columns).
Certain prefixes (co-, pre-, mid-, de-, non-, anti-, etc.) may or may not be hyphenated. Many long-established words, such as preamble and degrade, do not require a hyphen since the prefix is viewed as fully fused. In other cases, usage varies depending on individual or regional preference eg in English we say pre-schoo. A hyphen is mandatory when a prefix is applied to a proper (capitalized) adjective (un-American, de-Stalinisation). Hyphens may be employed where readers would otherwise be tempted into a mispronunciation (eg co-worker is so punctuated partly to prevent the reader’s eye being caught automatically by the word cow).
When a compound modifier other than an adverb-adjective appears before a term, the compound modifier is often hyphenated to prevent misunderstanding, such as in American-football player or real-world example. Without the hyphen, there is potential confusion about whether American applies to football or player, or whether the author might perhaps be referring to a “world example” that is “real”. Compound modifiers can extend to three or more words, as in ice-cream-flavored candy, and can be adverbial as well as adjectival (spine-tinglingly frightening).
Hyphens should normally not be used in adverb–adjective modifiers such as wholly owned subsidiary and quickly moving vehicle, because the adverbs clearly modify the adjectives; “quickly” cannot modify “vehicle”. Hyphens are used to connect numbers and words in forming adjectival phrases (particularly with weights and measures), whether using numerals or words for the numbers, as in 28-year-old woman and twenty-eight-year-old woman or 320-foot wingspan. The same usually holds for abbreviated time units. Hyphens are also used in spelled-out fractions as adjectives (but not as nouns), such as two-thirds majority and one-eighth portion.
An en-dash ( – ) sometimes replaces the hyphen in hyphenated compounds if either of its constituent parts is already hyphenated or contains a space (e.g. high-priority–high-pressure tasks (tasks which are both high-priority and high-pressure). En dashes are more proper than hyphens in ranges (pp. 312–14), relationships (blood–brain barrier) and to convey the sense of “to”, as in Nottingham-Lincoln race.