c.1300 (transitive), "to turn someone aside from a right religious belief to a false or erroneous one," from Old French pervertir "pervert, undo, destroy" (12c.) and directly from Latin pervertere "overthrow, overturn," figuratively "to corrupt, subvert, abuse," literally "turn the wrong way, turn about," from per- "away" (see per) + vertere "to turn" (see versus).
Related: Perverted; perverting. Replaced native froward, which embodies the same image. Old English had mishweorfed "perverted, inverted," an identical formation to the Latin word using native elements.
1660s, "one who has forsaken a doctrine or system regarded as true, apostate," from pervert (v.). Psychological sense of "one who has a perversion of the sexual instinct" is attested from 1897 (Havelock Ellis), originally especially of homosexuals.