halibut , holibut
n pl , -buts, -but
1 the largest flatfish: a dark green North Atlantic species, Hippoglossus hippoglossus, that is a very important food fish: family Pleuronectidae
2 any of several similar and related flatfishes, such as Reinhardtius hippoglossoides (Greenland halibut)
(C15: from hali holy (because it was eaten on holy days) + butte flat fish, from Middle Dutch butte)