From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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]