An idiolect (sometimes misspelled ideolect) is a variety of a language unique to an individual. It is manifested by patterns of word selection and grammar, or words, phrases or idioms that are unique to that individual. Every individual has an idiolect; the grouping of words and phrases is unique, rather than an individual using specific words that nobody else uses. An idiolect can easily evolve into an ecolect—a dialect variant specific to a household.

While often passing unnoticed in speech, some idiolects, particularly unusual ones employed by famous individuals, are immortalized in the form of nicknames. Famous examples include the nicknames of Ernesto "Che" Guevara and Willie Mays ("the Say-Hey Kid"), who frequently used the words "che" and "say hey" respectively.

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• Catch phrase