Idiom dictionary

An idiom 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 are very basic to the language, and qualify as conceptual metaphors without which English is quite hard to understand, e.g. "time as a substance", "time as a path", "love as war". These metaphors are often assumed in idioms, e.g. "battle of the sexes", "out of time".

Idiom dictionaries, as well as dictionaries in general, always rely on a defining vocabulary of terms (Longman's uses 2000) which are used only in their simplest senses, to minimize the number of such basic conceptual metaphors and polymorphic word uses, and make definitions easier for someone unfamiliar with the language to comprehend, such as children or students of English as an additional language.