The Collaborative International Dictionary of English v.0.48:

Cusk \Cusk\ (k[u^]sk), n. (Zool.)
   A large, edible, marine fish (Brosmius brosme), allied to
   the cod, common on the northern coasts of Europe and America;
   -- called also tusk and torsk.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cusk
    n 1: the lean flesh of a cod-like fish of North Atlantic waters
    2: large edible marine fish of northern coastal waters; related
       to cod [syn: cusk, torsk, Brosme brosme]
    3: elongate freshwater cod of northern Europe and Asia and North
       America having barbels around its mouth [syn: burbot,
       eelpout, ling, cusk, Lota lota]