The Collaborative International Dictionary of English v.0.48:

Burgomaster \Bur"go*mas`ter\, n. [D. burgemeester; burg borough
   + meester master; akin to G. burgemeister, b["u]rgermeister.
   See 1st Borough, and Master.]
   1. A chief magistrate of a municipal town in Holland,
      Flanders, and Germany, corresponding to mayor in England
      and the United States; a burghmaster.
      [1913 Webster]

   2. (Zool.) An aquatic bird, the glaucous gull (Larus
      glaucus), common in arctic regions.
      [1913 Webster]

WordNet (r) 3.0 (2006):

burgomaster
    n 1: a mayor of a municipality in Germany or Holland or Flanders
         or Austria

Bouvier's Law Dictionary, Revised 6th Ed (1856):

BURGOMASTER. In Germany this is, the title by which an officer who performs
the duties of a mayor is, called.