Mithraism vs religion

Mithraism and religion both are nouns.

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

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

Mithraism: ancient Persian religion; popular among Romans during first three centuries a.d.
religion: a strong belief in a supernatural power or powers that control human destiny

Other hypernyms of Mithraism include faith, religious belief.

Mithraism (noun)	religion (noun)
ancient Persian religion; popular among Romans during first three centuries a.d.	a strong belief in a supernatural power or powers that control human destiny
	an institution to express belief in a divine power