The Collaborative International Dictionary of English v.0.48:

Dunbird \Dun"bird`\, n. [Named from its color.] (Zool.)
   (a) The pochard; -- called also dunair, and dunker, or
       dun-curre.
   (b) An American duck; the ruddy duck.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dunker \Dun"ker\, prop. n. [G. tunken to dip.]
   One of a religious denomination whose tenets and practices
   are mainly those of the Baptists, but partly those of the
   Quakers; -- called also Tunkers, Dunkards, Dippers,
   and, by themselves, Brethren, and German Baptists, and
   they call their denomination the Church of the Brethren.
   [1913 Webster]

   Note: The denomination was founded in Germany in 1708, but
         after a few years the members emigrated to the United
         States; they were opposed to military service and
         taking legal oaths, and practiced trine immersion.
         [1913 Webster + WordNet 1.5]

   Seventh-day Dunkers, a sect which separated from the
      Dunkers and formed a community, in 1728. They keep the
      seventh day or Saturday as the Sabbath.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dunker
    n 1: an eater who dips food into a liquid before eating it; "he
         was a dunker--he couldn't eat a doughnut without a cup of
         coffee to dunk it in"
    2: a basketball player who is able to make dunk shots
    3: an adherent of Baptistic doctrines (who practice baptism by
       immersion) [syn: Dunker, Dunkard, Tunker]