hyphen

A number of compound words and phrases are joined by hyphens: thirty-seven;well-wisher;old-fashioned;mother-in-law. For some the hyphens are optional, or inserted only when the word or phrase is used before a noun: a coffee-table book;a well-timed attack (but the book on the coffee table;if the attack is well timed). Most words with prefixes do not have a hyphen, exceptions being those where a capital letter follows the prefix (e.g., pre-Christian) and those where the word could be confused with another (e.g., re-form meaning "form again" as distinct from reform). A hyphen is sometimes inserted when a prefix ending in a vowel is added to a word beginning with a vowel (e.g., co-opt,de-ice). In writing and printing, a hyphen may also be used to show that a word has been broken at the end of a line. Note that the word must be divided between syllables (e.g., stream-ing, not stre-aming) and the hyphen is attached to the end of the first part, not the beginning of the second part. Ideally there should be at least two letters in each part of the divided word.