Noun | 1. | Shiah Islam - one of the two main branches of orthodox Islam; mainly in Iran Islam, Muslimism - the civilization of Muslims collectively which is governed by the Muslim religion; "Islam is predominant in northern Africa, the Middle East, Pakistan, and Indonesia" Shia Muslim, Shiite, Shi'ite, Shiite Muslim, Shi'ite Muslim - a member of the branch of Islam that regards Ali as the legitimate successor to Mohammed and rejects the first three caliphs |