old master vs Nicolas Poussin

old master and Nicolas Poussin both are nouns.

Word	Noun	Adjective	Verb	Adverb
old master	Yes	No	No	No
Nicolas Poussin	Yes	No	No	No

old master (noun)	Nicolas Poussin (noun)
a great European painter prior to 19th century	French painter in the classical style (1594-1665)