Mithraism vs Mithraicism

Mithraism and Mithraicism both are nouns.

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

As nouns, Mithraism and Mithraicism are synonyms defined as:

Mithraism and Mithraicism: ancient Persian religion; popular among Romans during first three centuries a.d.

Mithraism (noun)	Mithraicism (noun)
ancient Persian religion; popular among Romans during first three centuries a.d.	ancient Persian religion; popular among Romans during first three centuries a.d.