Source : Webster's Revised Unabridged Dictionary (1913)

Halfbeak \Half"beak`\, n. (Zo["o]l.)
   Any slender, marine fish of the genus {Hemirhamphus}, having
   the upper jaw much shorter than the lower; -- called also
   {balahoo}.

Source : WordNet®

halfbeak
     n : tropical and subtropical marine and freshwater fishes having
         an elongated body and long protruding lower jaw