unison

Etymology

From Middle English unisoun, from Middle French unisson, from Medieval Latin ūnisonus (“having the same sound”), from ūni- + sonus (“sound”).

noun

1. (music, acoustics) Identical pitch between two notes or sounds; the simultaneous playing of notes of identical pitch (or separated by one or more octaves).
   The unison has a pitch ratio of 1:1.
   The young principal timpanist, Timothy Genis, was superb throughout, though his sidekick timpanist sometimes lagged in the final unisons. July 16, 2007, James R. Oestreich, “With Levine as Tour Guide, a Journey Through Mahler’s Third Symphony”, in New York Times
2. (music, acoustics) A sound or note having the same pitch as another, especially when used as the base note for an interval; a unison string.
3. The state of being in harmony or agreement; harmonious agreement or togetherness, synchronisation.
   Everyone moved in unison, but the sudden change in weight distribution capsized the boat.
4. (by extension) Two or more voices speaking the same words together.