Gregory the Great vs Roman Catholic

Gregory the Great and Roman Catholic both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gregory the Great	Yes	No	No	No
Roman Catholic	Yes	Yes	No	No

Gregory the Great (noun)	Roman Catholic (noun)
(Roman Catholic Church) an Italian pope distinguished for his spiritual and temporal leadership; a saint and Doctor of the Church (540?-604)	the Christian Church based in the Vatican and presided over by a pope and an episcopal hierarchy
	a member of the Roman Catholic Church

Gregory the Great (adjective)	Roman Catholic (adjective)
	of or relating to or supporting Romanism