The Collaborative International Dictionary of English v.0.48:

Anabaptist \An`a*bap"tist\, n. [LL. anabaptista, fr. Gr. as if
   'anabaptisth`s: cf. F. anabaptiste.]
   A name sometimes applied to a member of any sect holding that
   rebaptism is necessary for those baptized in infancy.
   [1913 Webster]

   Note: In church history, the name Anabaptists usually
         designates a sect of fanatics who greatly disturbed the
         peace of Germany, the Netherlands, etc., in the
         Reformation period. In more modern times the name has
         been applied to those who do not regard infant baptism
         as real and valid baptism.
         [1913 Webster] Anabaptistic

WordNet (r) 3.0 (2006):

Anabaptist
    n 1: adherent of Anabaptism