In everyday speech, a phrase may be any group of words, often carrying a special idiomatic meaning; in this sense it is roughly synonymous with expression. In linguistic analysis, a phrase is a group of words (or possibly a single word) that functions as a constituent in the syntax of a sentence—a single unit within a grammatical hierarchy. A phrase appears within a clause, although it is also possible for a phrase to be a clause or to contain a clause within it.