polyphony (n.)

1828, "multiplicity of sounds," from Greek polyphōnia "variety of sounds," from polyphōnos "having many sounds or voices," from polys "many" (from PIE root *pele- (1) "to fill") + phōnē "voice, sound," from PIE root *bha- (2) "to speak, tell, say." The musical meaning "act or process of simultaneously combining two or more voice parts so that they harmonize with each other but maintain their individuality" (1864) is perhaps a back-formation from the adjective. Related: Polyphonal.