an ancient Persian religion in which Mithras was worshiped, involving secret rituals to which only men were admitted: a major competitor of Christianity in the Roman empire during the 2nd and 3rd centuries a.d.
Mith·ra·ism (mĭth'rə-ĭz'əm, -rā-) n. A religious cult that worshiped Mithras, especially popular among the Roman military and a strong rival to Christianity during the late Roman Empire. Mith·ra'ic (mĭ-thrā'ĭk) adj., Mith·ra'ist n.