An iiom dictionary explains idiosyncratic stock phrases and metaphors in language. Typical English idiom dictionaries, e.g. that published by Longmans, define about 4000 phrases, e.g. "buy the farm", "hit the road", "canary in a coal mine". Of these, a tiny subset, generally involving prepositions or action verbs, are very basic to the language, and are closely related to fundamental conceptual metaphors. These include forms like out of or turn into.