Western Church vs Roman Catholic

Western Church and Roman Catholic both are nouns.

Word	Noun	Adjective	Verb	Adverb
Western Church	Yes	No	No	No
Roman Catholic	Yes	Yes	No	No

As nouns, Western Church and Roman Catholic are synonyms defined as:

Western Church and Roman Catholic: the Christian Church based in the Vatican and presided over by a pope and an episcopal hierarchy

Other synonyms of Western Church include Church of Rome, Roman Catholic Church, Roman Church.

Western Church (noun)	Roman Catholic (noun)
the Christian Church based in the Vatican and presided over by a pope and an episcopal hierarchy	the Christian Church based in the Vatican and presided over by a pope and an episcopal hierarchy
	a member of the Roman Catholic Church

Western Church (adjective)	Roman Catholic (adjective)
	of or relating to or supporting Romanism