The Collaborative International Dictionary of English v.0.48:

Margrave \Mar"grave\, n. [G. markgraf, prop., lord chief justice
   of the march; mark bound, border, march + graf earl, count,
   lord chief justice; cf. Goth. gagr["e]fts decree: cf. D.
   markgraaf, F. margrave. See March border, and cf.
   Landgrave, Graff.]
   1. Originally, a lord or keeper of the borders or marches in
      Germany.
      [1913 Webster]

   2. The English equivalent of the German title of nobility,
      markgraf; a marquis.
      [1913 Webster]

WordNet (r) 3.0 (2006):

margrave
    n 1: the military governor of a frontier province in medieval
         Germany
    2: a German nobleman ranking above a count (corresponding in
       rank to a British marquess)