Full admiral
Admiral is one of the highest naval ranks in some navies, and in many navies is the highest rank. It is usually abbreviated to "Adm" or "ADM". The rank is generally thought to have originated in Sicily from a conflation of Arabic: أمير البحر, amīr al-baḥr, "commander of the sea", with Latin admirabilis ("admirable") or admiratus ("admired"), although alternative etymologies derive the word directly from Latin, or from the Turkish military and naval rank miralay.
In the Commonwealth and the U.S., a "full" admiral is equivalent to a "full" general in the army, and is above vice admiral and below admiral of the fleet (or fleet admiral). In NATO, admirals have a rank code of OF-9 as a four-star rank.
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 12th 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".
...
Wikipedia