portraitist vs painter

portraitist and painter both are nouns.

Word	Noun	Adjective	Verb	Adverb
portraitist	Yes	No	No	No
painter	Yes	No	No	No

As nouns, painter is a hypernym of portraitist; that is, painter is a word with a broader meaning than portraitist:

portraitist (noun)	painter (noun)
a painter or drawer of portraits	large American feline resembling a lion
	a line that is attached to the bow of a boat and used for tying up (as when docking or towing)
	an artist who paints
	a worker who is employed to cover objects with paint