accompaniment

noun

musical parts which provide the rhythmic and/or harmonic support for the melody or main themes of a song or instrumental piece
going along; sociative action

Pronunciation: /əˈkʌm.pə.ni.mənt/ / /əˈkʌmp.ni.mənt/

Etymology: From French accompagnement; equivalent to accompany + -ment. First attested in 1744.

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.”
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.”
“forecasting torrential rain, with an accompaniment of crashing thunder.”