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c.1200, as an adjective, from Old French desconfit "vanquished, defeated," past participle of desconfire "to defeat, destroy," from des- "not" (see dis-) + confire "make, prepare, accomplish," from Latin conficere (see confection).
Used as a verb in English from c.1300. Weaker sense of "disconcert" is first recorded 1520s in English, probably by confusion with discomfort. Related: Discomfited; discomfiting.