pianist vs musician

pianist and musician both are nouns.

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

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

Other hypernyms of pianist include instrumentalist, player.

pianist (noun)	musician (noun)
a person who plays the piano	artist who composes or conducts music as a profession
	someone who plays a music as a profession