1.noun(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."
2.noun(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.nounThe 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."