1. [n]  a British peer of the highest rank
2. [n]  a nobleman (in various countries) of high rank

Duke
A biography of John Wayne, the iconic male hero of classic American cinema and an enduring figure in popular culture. Davis culls information from more than 65 interviews, extensive research, articles, and an extensive collaboration with Wayne`s agen...

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1. \Duke\n. [F. duc, fr. L. dux, ducis, leader, commander, fr.
   ducere to lead; akin to AS. te['o]n to draw; cf. AS. heretoga
   (here army) an army leader, general, G. herzog duke. See
   {Tue}, and cf. {Doge}, {Duchess}, {Ducat}, {Duct}, {Adduce},
   {Deduct}.]
   1. A leader; a chief; a prince. [Obs.]
            Hannibal, duke of Carthage.           --Sir T.
                                                  Elyot.
            All were dukes once, who were ``duces'' -- captains
            or leaders of their people.           --Trench.
   2. In England, one of the highest order of nobility after
      princes and princesses of the royal blood and the four
      archbishops of England and Ireland.
   3. In some European countries, a sovereign prince, without
      the title of king.
   {Duke's coronet}. See {Illust}. of {Coronet}.
   {To dine with Duke Humphrey}, to go without dinner. See under
      {Dine}.
   

2. \Duke\, v. i.
   To play the duke. [Poetic]
         Lord Angelo dukes it well in his absence. -- Shak.
   

derived from the Latin dux, meaning "a leader;" Arabic, "a sheik." This word is used to denote the phylarch or chief of a tribe (Gen. 36:15-43; Ex. 15:15; 1 Chr. 1:51-54).