flatfish - any of several families of fishes having flattened bodies that swim along the sea floor on one side of the body with both eyes on the upper sideflounder - any of various European and non-European marine flatfish holibut, halibut - marine food fish of the northern Atlantic or northern Pacific; the largest flatfish and one of the largest teleost fishes tongue-fish, tonguefish - left-eyed marine flatfish whose tail tapers to a point; of little commercial value sole - right-eyed flatfish; many are valued as food; most common in warm seas especially European |