Mithraism Syllabification: (Mith·ra·ism)Pronunciation: /ˈmiTHrəˌizəm/Definition of Mithraism noun the cult of the god Mithras, which became popular among Roman soldiers of the later empire, and was the main rival to Christianity in the first three centuries ad. Derivatives MithraicPronunciation: /miˈTHrā-ik/ adjective MithraistPronunciation: /miˈTHrā-ist/ noun Mithraism in other Oxford dictionaries Definition of Mithraism in the British & World English dictionary