A compoun modifier (also called a compound adjective or a phrasal adjective) is an adjectival or adverbial phrase of two or more words. According to modern writing guides, compound modifiers require a hyphen between each word (not between the phrase and the noun the phrase modifies). Hyphens help prevent confusion; otherwise, a reader might interpret the words separately, rather than as a phrase. One or more hyphens join the words into a single idea.