"one who has the authority or power to command or order," early 14c., comandur, from Old French comandeor "commander, commandant," from comander "to order, enjoin" (see command (v.)). Commander in chief "commander of all the armies of a state" is attested from 1650s. In the U.S., by the Constitution, it is the president; George Washington was so called by 1778.
"commanding naval officer," 1690s, probably via Dutch kommandeur from French commandeur, from Old French comandeor (see commander). The U.S. Navy rank was created 1862, above a captain, below a rear-admiral.
"a dean, the senior member of a body," originally "a commander of ten," early 15c., from Old French doyen "commander of ten," from Old French deien (see dean).
c. 1200, amiral, admirail, "Saracen commander or chieftain," from Old French amirail (12c.) "Saracen military commander; any military commander," ultimately from medieval Arabic amir "military commander," probably via Medieval Latin use of the word for "Muslim military leader."
Amiral de la mer "commander of a fleet of ships" is in late 13c. Anglo-French documents. Meaning "highest-ranking naval officer" in English is from early 15c. The extension of the word's meaning from "commander on land" to "commander at sea" likely began in 12c. Sicily with Medieval Latin amiratus and then spread to the continent, but the word also continued to mean "Muslim military commander" in Europe in the Middle Ages. The Arabic word was later Englished as emir.
As amīr is constantly followed by -al- in all such titles, amīr-al- was naturally assumed by Christian writers as a substantive word, and variously Latinized .... [OED]
Also in Old French and Middle English the word was further conformed to familiar patterns as amirauld, amiraunt. The unetymological -d- probably is from influence of Latin ad-mirabilis (see admire). Italian form almiraglio, Spanish almirante are from confusion with Arabic words in al-. As the name of a type of butterfly from 1720, according to OED possibly a corruption of admirable.
among Arabic or Muslim peoples, "chief of a family or tribe; a ruling prince," 1590s, from Arabic amir "commander" (see admiral).
"absolute ruler," 1580s, from Latin imperator "commander-in-chief, leader, master," agent noun from stem of imperare "to command" (see imperative (adj.)). In the Roman republic, a holder of military command during active service, also a title bestowed on victorious generals; in the Roman Empire, the emperor as commander-in-chief of the armies. Related: Imperatorial.
early 15c., "belonging to the Praetorian Guard," from Latin praetorianus "belonging to a praetor," from praetor (see praetor). Praetorian Guard translates cohors praetoria, the bodyguard troop of a Roman commander or emperor. Hence modern figurative use for "defenders of an existing order."
masc. proper name, name of Saul's commander in the Old Testament, from Hebrew Abhner, literally "my father is light," from abh "father" + ner "light."