[flat-fish] 
) -fish, (especially referring to two or more kinds or species) -fish⋅es. | any fish of the order Heterosomata (Pleuronectiformes), including the halibut, sole, flounder, etc., having a greatly compressed body and swimming on one side, with both eyes on the upper side in the adult. |
| flat·fish (flāt'fĭsh') n. pl. flatfish or flat·fish·es Any of numerous chiefly marine fishes of the order Pleuronectiformes, including the flounders, soles, and halibuts, having a laterally compressed body with both eyes on the upper side. |