dukeyoudaoicibaDictYouDict[duke 词源字典]
duke: [12] Duke is one of a wide range of English words which come ultimately from the Latin verb dūcere ‘lead’ (see DUCT). In this case its source was the Latin derivative dux ‘leader’ (ancestor also of Italian duce, the title adopted by the 20th-century dictator Benito Mussolini), which passed into English via Old French duc. In Latin the word signified ‘military commander of a province’, and in the so-called Dark Ages it was taken up in various European languages as the term for a ‘prince ruling a small state’.

Old English never adopted it though, preferring its own word earl, and it was not until the 14th century that it was formally introduced, by Edward III, as a rank of the English peerage. Before that the word had been used in English only in the titles of foreign dukes, or (echoing the word’s etymological meaning) as a general term for ‘leader’ or ‘military commander’. The feminine form duchess [14] comes from Old French, while English has two terms for a duke’s rank or territory: the native dukedom [15], and duchy [14], borrowed from Old French duche (this came partly from medieval Latin ducātus, ultimate source of English ducat [14], a former Italian coin).
=> conduct, ducat, duchess, duchy, duct, produce[duke etymology, duke origin, 英语词源]
duke (n.)youdaoicibaDictYouDict
early 12c., "sovereign prince," from Old French duc (12c.) and directly from Latin dux (genitive ducis) "leader, commander," in Late Latin "governor of a province," from ducere "to lead," from PIE *deuk- "to lead" (cognates: Old English togian "to pull, drag," Old High German ziohan "to pull," Old English togian "to draw, drag," Middle Welsh dygaf "I draw").

Applied in English to "nobleman of the highest rank" probably first mid-14c., ousting native earl. Also used to translate various European titles (such as Russian knyaz).