Meaning

noun lean flesh of very large flatfish of Atlantic or Pacific

noun marine food fish of the northern Atlantic or northern Pacific; the largest flatfish and one of the largest teleost fishes

originFrom Middle English *halibutt, equivalent to holy + but (“flatfish”), since the fish was often eaten on holy days. Cognate with Dutch heilbot, German Heiligbutt, Heilbutt, Heilbutte, Danish helleflynder, Swedish helgeflundra, and Norwegian Nynorsk hellefisk.

Etymology from Wiktionary, CC BY-SA 3.0