duke

Duke is a male title either of a monarch ruling over a duchy, or of a member of royalty, or nobility. As rulers, dukes are ranked below emperors, kings, grand princes, grand dukes, and above sovereign princes. As royalty or nobility, they are ranked below grand dukes and above or below princes, depending on the country or specific title. The title comes from French duc, itself from the Latin dux, 'leader', a term used in republican Rome to refer to a military commander without an official rank, and later coming to mean the leading military commander of a province. In most countries, the word duchess is the female equivalent. thumb|A portrait of James Brydges, 1st Duke of Chandos wearing the [[robes of the British peerage.]] Following the reforms of the emperor Diocletian (which separated the civilian and military administrations of the Roman provinces), a dux became the military commander in each province. The title dux, Hellenised to doux, survived in the Eastern Roman Empire where it continued in several contexts, signifying a rank equivalent to a captain or general. Later on, in the 11th century, the title Megas Doux was introduced for the post of commander-in-chief of the entire navy.

During the Middle Ages, the title (as Herzog) signified first among the Germanic monarchies. Dukes were the rulers of the provinces and the superiors of the counts in the cities and later, in the feudal monarchies, the highest-ranking peers of the king. A duke may or may not be, ipso facto, a member of the nation's peerage: in the United Kingdom and Spain, all dukes are/were also peers of the realm, in France, some were and some were not, while the term is not applicable to dukedoms of other nations, even where an institution similar to the peerage (e.g. Grandeeship, Imperial Diet, Hungarian House of Magnates) existed.