The link hyphenThe use of the hyphen to mark COMPOUND WORDS has existed in English since the 16c, and from an earlier date in various forms in words such as to-day and with-out. It has always been variable and unpredictable. In recent use, it appears to be diminishing in some circumstances: for example, when the elements of a compound are monosyllabic (birdsong, eardrum, playgroup; lambswool, formerly lamb's wool), in longer formations where the elements are regarded as closely associated (business-woman, nationwide); where the two elements are regarded as having equal semantic weight, with the first acting as a modifier, forming a spaced pair (road sign, snow goose); and in prefixed forms such as coordinate and reuse. The absence of the hyphen in such cases is well established in AmE, and is becoming more common in BrE. The hyphen continues in BrE and AmE in both routine and occasional couplings when the elements seem to retain a stronger individual identity, and in ad-hoc formations: boiler-room, filling-station. In the second of these, filling is a noun (‘a station for filling’) and not a participle (‘a station that fills’), which the absence of a hyphen might imply. Usage, however, is rarely consistent or completely logical in this regard. A hyphen is often retained to avoid awkward collisions of letters, as in breast-stroke, co-worker, and radio-isotope, but usage varies even in these cases, often in keeping the elements of compounds separate (breast stroke, radio isotope), and occasionally merging them (breaststroke, radioisotope).
The link hyphen also has a role in punctuation: (1) To establish such syntactic links as truck-driver, labour-saving, and brown-eyed. In the phrases hard-covered books and French-speaking visitors, the reference is to ‘books with hard covers’ and ‘visitors who speak French’; here, hyphenation prevents misunderstanding and parallels the stress patterns of speech: hárd-covered bóoks and Frénch-speaking péople as opposed to hard cóvered bóoks and French spéaking péople. (2) To form expression with a phrasal base, such as drink-affected (affected by drink), weed-infested (infested with weeds), and panic-stricken (stricken by panic). (3) To avoid ambiguity in twenty-odd people (compare twenty odd people). (4) To connect the elements of associated words used attributively as in a well-known woman and Christmas-tree lights, but not predicatively as in the woman is well known and the lights on the Christmas tree. (5) Connecting nouns in apposition that form a single concept, such as city-state (a city that is also a state) and player-manager (a manager who is also a player), and in units such as passenger-mile (a mile travelled by one passenger: a statistical usage). (6) Connecting elements to form words in cases such as re-enact (where the collision of the first and second e might be awkward), re-form (meaning ‘to form again’ as opposed to reform), and some prefixed words such as those in anti-, non-, over-, and past-. Usage varies in this regard, especially as between BrE and AmE. In AmE, solid forms such as reenact and nonstandard are common. In general terms, a great deal depends on how established and recognizable a formation is: when the second element begins with a capital letter, a hyphen is usual, as in anti-Darwinian. There are no hard-and-fast rules.
The break hyphenThe hyphen is used to divide a word at the end of a line, especially in print when words are spaced out to fill lines with justified margins. In handwritten texts, typed or word-processed material, and unjustified print, word-breaks can usually be avoided. In print, it has traditionally been a matter of pride with printers and publishers to ensure a careful division of words when line-breaks occur, taking account of the appearance and structure of the word. There are two basic approaches, phonetic (in terms of syllable structure) and morphological (in terms of word structure). Broadly, AmE favours a phonetic approach (preferring trium-phant to triumph-ant), while BrE has usually given greater weight to a morphological approach, although preferences are widely varied (veg-etable, vege-table, ve-getable). Newspapers in all English-speaking countries tend to produce word divisions that reflect neither criterion (such as bat-hroom, se-arched, da-ily), usually because the line-breaks in their computer typesetting programs are based on fairly crude principles such as division between two consonants. The traditional aim of word division at line-breaks is to distract the reader as little as possible. See DIAERESIS, OBLIQUE, PHRASE WORD, SENTENCE WORD, SYLLABICATION.
hy·phen / ˈhīfən/ • n. the sign (-) used to join words to indicate that they have a combined meaning or that they are linked in the grammar of a sentence (as in pick-me-up, rock-forming), to indicate the division of a word at the end of a line, or to indicate a missing or implied element (as in short- and long-term). • v. another term for hyphenate. ORIGIN: early 17th cent.: via late Latin from Greek huphen ‘together,’ from hupo ‘under’ + hen ‘one.’
Hence hyphen vb., hyphenate XIX.