halibut
Concise Oxford English Dictionary © 2008 Oxford University Press:
halibut /ˈhalɪbət/
▶noun (pl. same) a large marine flatfish, used as food. [Hippoglossus hippoglossus (N. Atlantic), H. stenolepis (N. Pacific), and other species.]
– origin ME: from haly ‘holy’ + obs. butt ‘flatfish’ (because it was often eaten on holy days).
'halibut' also found in these Oxford entries:

