Case: it involves singular person on the fiddle?

• Tuba player, e.g.
• Helpful to first violinist for example
• Tuba player, e.g
• Helpful first violinist?
• One just plays at work
• One who plays without vocals

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Instrumentalism \In`stru*men"tal*ism\, n. (Philos.) The view that the sanction of truth is its utility, or that truth is genuine only in so far as it is a valuable instrument. -- In`stru*men"tal*ist , n. Instrumentalism views truth as simply the value belonging ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1823, from instrumental in the musical sense + -ist .

WordNet Word definitions in WordNet
n. someone who plays a musical instrument (as a profession) [syn: musician , player ]