Romanism vs Roman Catholicism

Romanism and Roman Catholicism both are nouns.

Word	Noun	Adjective	Verb	Adverb
Romanism	Yes	No	No	No
Roman Catholicism	Yes	No	No	No

As nouns, Romanism and Roman Catholicism are synonyms defined as:

Romanism and Roman Catholicism: the beliefs and practices of the Catholic Church based in Rome

Other synonyms of Romanism include papism.

Romanism (noun)	Roman Catholicism (noun)
the beliefs and practices of the Catholic Church based in Rome	the beliefs and practices of the Catholic Church based in Rome