The Collaborative International Dictionary of English v.0.48:

Cowfish \Cow"fish`\ (kou"f[i^]sh`), n. (Zool.)
   (a) The grampus.
   (b) A California dolphin (Tursiops Gillii).
   (c) A marine plectognath fish (Ostracoin quadricorne, and
       allied species), having two projections, like horns, in
       front; -- called also cuckold, coffer fish,
       trunkfish.
       [1913 Webster]