The word admiral in Middle English comes from Anglo-French amiral, "commander", from Medieval Latin admiralis, admirallus. These themselves come from Arabic amīr, or amīr al- (أمير الـ), "commander of", as in amīr al-baḥr (أمير البحر), "commander of the sea". The term was in use for the Greco-Arab naval leaders of Norman Sicily, which had formerly been ruled by Arabs, at least by the early 11th century.
The Norman Roger II of Sicily (1095–1154), employed a Greek Christian known as George of Antioch, who previously had served as a naval commander for several North African Muslim rulers. Roger styled George in Abbasid fashion as Amir of Amirs, i.e. "Commander of Commanders", with the title becoming Latinized in the 13th century as ammiratus ammiratorum.
The Sicilians and later Genoese took the first two parts of the term and used them as one word, amiral, from their Aragon opponents. The French and Spanish gave their sea commanders similar titles while in Portuguese the word changed to almirante. As the word was used by people speaking Latin or Latin-based languages it gained the "d" and endured a series of different endings and spellings leading to the English spelling admyrall in the 14th century and to admiral by the 16th century.