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1580s, from Middle French catégorie, from Late Latin categoria, from Greek kategoria "accusation, prediction, category," verbal noun from kategorein "to speak against; to accuse, assert, predicate," from kata "down to" (or perhaps "against;" see cata-) + agoreuein "to harangue, to declaim (in the assembly)," from agora "public assembly" (see agora). Original sense of "accuse" weakened to "assert, name" by the time Aristotle applied kategoria to his 10 classes of things that can be named.
category should be used by no-one who is not prepared to state (1) that he does not mean class, & (2) that he knows the difference between the two .... [Fowler]