polyphonic (adj.)

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.

of recordings, broadcasts, etc., "not stereo, having only one output signal," 1958, coined to be an opposite of stereophonic; from mono- "single" + -phonic, from Greek phōnē "sound, voice," from PIE root *bha- (2) "to speak, tell, say." It was used earlier in music, "pertaining to a style of composition in which one voice-part predominates over the others" (opposed to polyphonic), by 1885.