The megas doux (Greek: μέγας δούξ pronounced [ˈmeɣaz ˈðuks]; English: grand duke) was one of the highest positions in the hierarchy of the later Byzantine Empire, denoting the commander-in-chief of the Byzantine navy. It is sometimes also given by the half-Latinizations megaduke or megadux (from Greek μεγαδούξ). The Greek word δούξ is the Hellenized form of the Latin term dux, meaning leader or commander.