moeurs (n.)

mid-14c., "associated with or characterized by right behavior," also "associated with or concerning conduct or moral principles" (good or bad), from Old French moral (14c.) and directly from Latin moralis "proper behavior of a person in society," literally "pertaining to manners," coined by Cicero ("De Fato," II.i) to translate Greek ethikos (see ethics) from Latin mos (genitive moris) "one's disposition," in plural, "mores, customs, manners, morals," a word of uncertain origin. Perhaps sharing a PIE root with English mood (n.1).

From late 14c. as "of or pertaining to rules of right conduct" (opposed to non-moral, amoral) and "morally good, in accordance with rules of right conduct" (opposed to immoral). Of persons, "habitually conforming to moral rules," 1630s. From 1680s with reference to rights, duties, etc., "founded on morality" (opposed to legal).

Applied to indirect effect in moral support (1823), moral victory (1888), where the notion is "pertaining to or affecting the character or conduct" (as distinguished from the intellectual or physical nature), a sense attested from 1590s; in this sense, compare morale. Related: Morally.