Source : Webster's Revised Unabridged Dictionary (1913)

Doge \Doge\, n. [It doge, dogio, for duce, duca, fr. L. dux,
   ducis, a leader, commander. See {Duke}.]
   The chief magistrate in the republics of Venice and Genoa.

Source : WordNet®

doge
     n : formerly the chief magistrate in the republics of Venice and
         Genoa