Mith·ra·ism 
(mĭthrə-ĭz′əm, -rā-)
(mĭthrə-ĭz′əm, -rā-)n.
A religion based on the worship of Mithras that was especially popular among the Roman military and a strong rival to Christianity during the late Roman Empire.
Mith·raic (mĭ-thrāĭk) adj.
Mith·raist n.