painter vs portraitist

painter and portraitist both are nouns.

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

As nouns, portraitist is a hyponym of painter; that is, portraitist is a word with a more specific, narrower meaning than painter:

painter (noun)	portraitist (noun)
large American feline resembling a lion	a painter or drawer of portraits
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