[uni.son] n [MF, fr. ML unisonus having the same sound, fr. L uni- + sonus sound--more at sound] (1575) 1 a: identity in musical pitch; specif: the interval of a perfect prime b: the state of being so tuned or sounded c: the writing, playing, or singing of parts in a musical passage at the same pitch or in octaves
2: a harmonious agreement or union: concord -- unison adj -- in unison 1: in perfect agreement: so as to harmonize exactly
2: at the same time: simultaneously