early 15c., dissonaunce, "disagreement, discrepancy, incongruity, inconsistency" (between things), from Old French dissonance and directly from Medieval Latin dissonantia, from Latin dissonantem, present participle of dissonare "differ in sound," from dis- "apart" (see dis-) + sonare "to sound, make a noise," from PIE *swene-, from root *swen- "to sound." Etymological sense, "inharmonious mixture or combination of sounds," is from 1590s in English.
