old master vs painter

old master and painter both are nouns.

Word	Noun	Adjective	Verb	Adverb
old master	Yes	No	No	No
painter	Yes	No	No	No

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

Other hypernyms of old master include maestro, master.

old master (noun)	painter (noun)
a great European painter prior to 19th century	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