Accompaniment

Noun

1. A part, usually performed by instruments, that gives support or adds to the background in music, or adds for ornamentation; also, the harmony of a figured bass.

   "Brooks performed a saxophone solo on stage, with Robert as accompaniment on the bass."

2. That which accompanies; something that attends as a circumstance, or which is added to give greater completeness to the principal thing, or by way of ornament, or for the sake of symmetry.

   "A side salad is a common accompaniment to a main dish."