The Collaborative International Dictionary of English v.0.48:

Whitefish \White"fish`\, n. (Zool.)
   (a) Any one of several species of Coregonus, a genus of
       excellent food fishes allied to the salmons. They inhabit
       the lakes of the colder parts of North America, Asia, and
       Europe. The largest and most important American species
       (Coregonus clupeiformis) is abundant in the Great
       Lakes, and in other lakes farther north. Called also
       lake whitefish, and Oswego bass.
   (b) The menhaden.
   (c) The beluga, or white whale.
       [1913 Webster]

   Note: Various other fishes are locally called whitefish, as
         the silver salmon, the whiting
   (a), the yellowtail, and the young of the bluefish
       (Pomatomus saltatrix).
       [1913 Webster]