A dialect or historical term for a type of fish, possibly a species of flounder or flatfish with a distinctive back coloration.
From butter (yellow or pale colored) plus back (upper surface). This is a folk etymology name, common in fishing communities where fish were named descriptively by appearance.
Fish names like 'butterback' are disappearing from English as we lose regional fishing dialects—each community had unique names for local fish that perfectly captured their appearance, and we're losing centuries of ecological observation.
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