A pact, an agreement.
To form a pact; to make a binding agreement.
The state of being in harmony or agreement; harmonious agreement or togetherness, synchronisation.
A sound or note having the same pitch as another, especially when used as the base note for an interval; a unison string.
Identical pitch between two notes or sounds; the simultaneous playing of notes of identical pitch (or separated by one or more octaves).
Two or more voices speaking the same words together.