Ancillary role of 2 Down

• Musician
• Helpful first violinist?
• Band member
• Helpful to first violinist for example
• Tuba player, e.g.
• Someone who plays a musical instrument (as a profession)
• Case: it involves singular person on the fiddle?

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Instrumentalist \In`stru*men"tal*ist\, n. One who plays upon an instrument of music, as distinguished from a vocalist .