romish vs Roman Catholic

romish is not a noun while Roman Catholic is a noun.

Word	Noun	Adjective	Verb	Adverb
romish	No	Yes	No	No
Roman Catholic	Yes	Yes	No	No

As adjectives, romish and Roman Catholic are synonyms defined as:

Other synonyms of romish include papist, papistic, papistical, popish, R.C., Roman, Romanist.

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

romish (adjective)	Roman Catholic (adjective)
of or relating to or supporting Romanism	of or relating to or supporting Romanism