Roman Catholicism vs Romanism

Roman Catholicism and Romanism both are nouns.

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

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

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

Other synonyms of Roman Catholicism include papism.

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