Admiral is one of the highest ranks in many navies. In the Commonwealth nations and the United States, a "full" admiral is equivalent to a "full" general in the army or the air force. Admiral is ranked above vice admiral and below admiral of the fleet, or fleet admiral.

The word admiral in Middle English comes from Anglo-French amiral, "commander", from Medieval Latin admiralis, admirallus. These evolved from the Arabic amīral (أمير الـ) – amīr (أمير) [ʔmjr] (listen^ⓘ), "king, prince, chief, leader, nobleman, lord, a governor, commander, or person who rules over a number of people" and al (الـ), the Arabic definite article meaning "the." In Arabic, admiral is also represented as Amīr al-Baḥr (أمير البحر), where al-Baḥr (البحر) means the sea.

The 1818 edition of Samuel Johnson's A Dictionary of the English Language, edited and revised by the Rev. Henry John Todd, states that the term:

[...] has been traced to the Arab. emir or amir, lord or commander, and the Gr. ἄλιος, the sea, q. d. prince of the sea. The word is written both with and without the d, in other languages, as well as our own. Barb. Lat. admirallus and amiralius. V. Ducange. Barb. Græc. ἄμηραλιος. V. Meursii Gloss. Græco-Barbarum, edit. 1610. p. 29. Fr. admiral and amiral. Dan. the same. Germ. ammiral. Dutch, admirael or ammirael. Ital. ammiraglio. Sp. almirante. Minsheu, in his Spanish Dictionary, says 'almiralle is a king in the Arabian language.' Amrayl is used by Robert of Gloucester, in the sense of a prince, or governour.

The quote from John Minsheu's Dictionarie in Spanish and English (1599), given in Johnson's Dictionary, has been confirmed as being accurate. Additionally, the definition of Amīr (أمير), as given in Edward William Lane's Arabic-English Lexicon, concurs, in part, with Minsheu's definition, stating that the term means "One having, holding, or possessing, command; a commander; a governor; a lord; a prince, or king."

While other Greek words of the period existed to indicate "belonging to the sea," or "of the sea," the now obsolete Gr. ἄλιος mentioned in Johnson's Dictionary is expressly defined as "of the sea, Lat. marinus, epith. of sea-gods, nymphs, etc."

Though there are multiple meanings for the Arabic Amīr (أمير), the literal meaning of the phrase Amīr al-Baḥr (أمير البحر) is "Prince of the Sea." This position, versus "commander of the sea," is demonstrated by legal practices prevailing in the Ottoman Empire, whereas it was only possible for Phanariots to qualify for attaining four princely positions, those being grand dragoman, dragoman of the fleet, and the voivodees of Moldavia and Wallachia. Those Phanariots who attained the princely position of dragoman of the fleet served under the Ottoman admiral having administration of the Aegean islands and the Anatolian coast.

Modern acknowledgement of the phrase Amīr-al-Baḥr (أمير البحر) meaning "Prince of the Sea" includes a speech made in an official U.S. military ceremony conducted in an Arabic port, and a news article published by an Arabic news outlet: On 24 May 2012, in a change of command ceremony aboard aircraft carrier USS Enterprise (CVN 65), while docked at Khalifa Bin Salman Port, Bahrain, U.S. Marine Corps Gen. James Mattis, Commander, U.S. Central Command, introduced Vice Admiral Mark I. Fox as "Admiral Fox, the prince of the sea, emir of the sea – to translate 'admiral' from the Arabic to English;" On 04 Feb 2021, in an announcement of his coronavirus-related death, the Arabic news website Saudi 24 News referred to Admiral Edmond Chagoury by the title "Prince of the Sea."