pianist vs instrumentalist

pianist and instrumentalist both are nouns.

Word	Noun	Adjective	Verb	Adverb
pianist	Yes	No	No	No
instrumentalist	Yes	No	No	No

As nouns, instrumentalist is a hypernym of pianist; that is, instrumentalist is a word with a broader meaning than pianist:

Other hypernyms of pianist include musician, player.

pianist (noun)	instrumentalist (noun)
a person who plays the piano	someone who plays a music as a profession