The Collaborative International Dictionary of English v.0.48:

Duke \Duke\ (d[=u]k), 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.]
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            Hannibal, duke of Carthage.           --Sir T.
                                                  Elyot.
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            All were dukes once, who were "duces" -- captains or
            leaders of their people.              --Trench.
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   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.
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   3. In some European countries, a sovereign prince, without
      the title of king.
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   4. pl. The fists; as, put up your dukes. [slang]
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   Duke's coronet. See Illust. of Coronet.

   To dine with Duke Humphrey, to go without dinner. See under
      Dine.
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