A duke (male) can either be a monarch ranked below the emperor, king, and grand duke ruling over a duchy or a member of royalty or nobility, historically of highest rank, below princes of nobility and grand dukes. 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.
