unisonyoudaoicibaDictYouDict
unison: [16] Unison originated as a musical term, denoting ‘of the same sound’. It comes via Old French unison from late Latin ūnisonus, a compound adjective formed from ūnus ‘one’ and sonus ‘sound’ (source of English sound). The metaphorical sense ‘agreement, concord’ emerged in the 17th century.
=> sound
unison (n.)youdaoicibaDictYouDict
1570s, "note having the same pitch as another; identity in pitch of two or more sounds; interval between tones of the same pitch," especially the interval of an octave, from Middle French unisson "unison, accord of sound" (16c.) or directly from Medieval Latin unisonus "having one sound, sounding the same," from Late Latin unisonius "in immediate sequence in the scale, monotonous," from Latin uni- "one" (see one) + sonus "sound" (see sound (n.1)). Figurative sense of "harmonious agreement" is first attested 1640s.