(idiomatic, rhetoric, logic, linguistics) A type of tautology in which an item is being explained in terms of the item itself, only put in different (usually more abstract) words.
A calque translation of Latin, virtus dormitiva, coined by Molière in The Imaginary Invalid. In the play, he lampoons a group of physicians providing an explanation in macaronic Latin of the sleep-inducing properties of opium as stemming from its "virtus dormitiva".
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