pagan religion vs paganism

pagan religion and paganism both are nouns.

Word	Noun	Adjective	Verb	Adverb
pagan religion	Yes	No	No	No
paganism	Yes	No	No	No

As nouns, pagan religion and paganism are synonyms defined as:

pagan religion and paganism: any of various religions other than Christianity or Judaism or Islamism

Other synonyms of pagan religion include heathenism.

pagan religion (noun)	paganism (noun)
any of various religions other than Christianity or Judaism or Islamism	any of various religions other than Christianity or Judaism or Islamism