The Collaborative International Dictionary of English v.0.48:

Forktail \Fork"tail`\, n. (Zool.)
   (a) One of several Asiatic and East Indian passerine birds,
       belonging to Enucurus, and allied genera. The tail is
       deeply forked.
   (b) A salmon in its fourth year's growth. [Prov. Eng.]
       [1913 Webster]