The Collaborative International Dictionary of English v.0.48:

Buffel duck \Buf"fel duck\ (b[u^]f"f[e^]l d[u^]k`). [See
   Buffalo.] (Zool.)
   A small duck (Charitonetta albeola); the spirit duck, or
   butterball. The head of the male is covered with numerous
   elongated feathers, and thus appears large. Called also
   bufflehead.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bufflehead \Buf"fle*head`\, n. [Buffle + head.]
   1. One who has a large head; a heavy, stupid fellow. [Obs.]
      [1913 Webster]

            What makes you stare so, bufflehead?  --Plautus
                                                  (trans. 1694).
      [1913 Webster]

   2. (Zool.) The buffel duck. See Buffel duck.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bufflehead
    n 1: small North American diving duck; males have bushy head
         plumage [syn: bufflehead, butterball, dipper,
         Bucephela albeola]