pagan religion vs heathenism

pagan religion and heathenism both are nouns.

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

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

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

Other synonyms of pagan religion include paganism.

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