The Collaborative International Dictionary of English v.0.48:

Bullhead \Bull"head`\, n.
   1. (Zool.)
      (a) A fresh-water fish of many species, of the genus
          Uranidea, esp. Uranidea gobio of Europe, and
          Uranidea Richardsoni of the United States; -- called
          also miller's thumb.
      (b) In America, several species of Amiurus; -- called
          also catfish, horned pout, and bullpout.
      (c) A marine fish of the genus Cottus; the sculpin.
          [1913 Webster]

   2. (Zool.)
      (a) The black-bellied plover (Squatarola helvetica); --
          called also beetlehead.
      (b) The golden plover.
          [1913 Webster]

   3. A stupid fellow; a lubber. [Colloq.] --Jonson.
      [1913 Webster]

   4. (Zool.) A small black water insect. --E. Phillips.
      [1913 Webster]

   Bullhead whiting (Zool.), the kingfish of Florida
      (Menticirrus alburnus).
      [1913 Webster]