n. & adj.
n. 1 Mus. a coincidence in pitch of sounds or notes. b this regarded as an interval. 2 Mus. a combination of voices or instruments at the same pitch or at pitches differing by one or more octaves (sang in unison). 3 agreement, concord (acted in perfect unison).
adj. Mus. coinciding in pitch. unison string a string tuned in unison with another string and meant to be sounded with it. unisonant adj. unisonous adj.
[ OF unison or LL unisonus (as UNI-, sonus SOUND(1)) ]