unison

Unison means all together on the same note — two or more voices or instruments performing the same pitch simultaneously. In orchestral contexts, unison can also refer to performers playing the same melody at octave intervals, which is called octave unison. Unison passages create a powerful, focused sound. An entire string section playing in unison produces a rich, unified tone that is both louder and more complex than a single instrument. Composers use unison for moments of particular strength or simplicity — the opening of Beethoven's Fifth Symphony is essentially a unison statement. Unison singing in choirs creates a primal, commanding effect.