A
duke (male) (
British English: or
American English: ) or
duchess (female) can either be a monarch ruling over a
duchy or a member of the
nobility, historically of highest rank below the
monarch. 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 (particularly one of
Germanic or
Celtic origin), and later coming to mean the leading military commander of a province.