religion vs belief

religion and belief both are nouns.

Word	Noun	Adjective	Verb	Adverb
religion	Yes	No	No	No
belief	Yes	No	No	No

As nouns, belief is a hypernym of religion; that is, belief is a word with a broader meaning than religion:

religion: a strong belief in a supernatural power or powers that control human destiny
belief: any cognitive content held as true

Other hypernyms of religion include supernatural virtue, theological virtue.

religion (noun)	belief (noun)
a strong belief in a supernatural power or powers that control human destiny	any cognitive content held as true
an institution to express belief in a divine power	a vague idea in which some confidence is placed