Case: it involves singular person on the fiddle?

• Musician
• Helpful to first violinist for example
• Someone who plays a musical instrument (as a profession)
• Tuba player, e.g.
• One who plays without vocals
• Tuba player, e.g

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM CORPUS ▪ All the instrumentalists, of course, weave solos through this fabric of sustained notes, but the focal point is Threadgill. ▪ First, the ballet livrets of this period treat the instrumentalists as members of discrete groups. ...

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 .

Wiktionary Word definitions in Wiktionary
n. One who plays a musical instrument, as distinguished from a vocalist