late 14c., from Old French armonie "harmony," also the name of a musical instrument (12c.), from Latin harmonia, from Greek harmonia "agreement, concord of sounds," also as a proper name, the personification of music, literally "means of joining," used of ship-planks, etc., also "settled government, order," related to harmos "fastenings of a door; shoulder," from PIE *ar-ti-, from *ar- "to fit together" (see arm, n.1). Musical sense is oldest in English; that of "agreement of feeling, concord" is from late 14c.