theism vs religious belief

theism and religious belief both are nouns.

Word	Noun	Adjective	Verb	Adverb
theism	Yes	No	No	No
religious belief	Yes	No	No	No

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

theism: the doctrine or belief in the existence of a God or gods
religious belief: a strong belief in a supernatural power or powers that control human destiny

Other hypernyms of theism include faith, religion.

theism (noun)	religious belief (noun)
the doctrine or belief in the existence of a God or gods	a strong belief in a supernatural power or powers that control human destiny