flatfish

UK: /ˈflætfɪʃ/ US: /ˈflætˌfɪʃ/ ,(flat′fish′)

Inflections of 'flatfish' (n):

flatfish

npl (Especially as a collective plural—e.g. "Flatfish can be found in all the world's oceans.")

flatfishes

npl (Mainly used to talk about different types—e.g. "Some flatfishes can camouflage themselves.")

WordReference Random House Learner's Dictionary of American English © 2025

flat•fish /ˈflætˌfɪʃ/   n., pl. (esp. when thought of as a group) -fish, (esp. for kinds or species) -fish•es. 

1. Fish any of various fishes, such as the flounders, that have as adults a greatly flattened body with both eyes on the upper side.

WordReference Random House Unabridged Dictionary of American English © 2025

flat•fish  (flat′fish′), n., pl. (esp. collectively) -fish,  (esp. referring to two or more kinds or species) -fish•es. 

1. Fish 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.

• flat¹ + fish 1700–10

Collins Concise English Dictionary © HarperCollins Publishers::

flatfish / ˈflætˌfɪʃ/ noun ( -fish, -fishes)

1. any marine spiny-finned fish of the order Heterosomata, including the halibut, plaice, turbot, and sole, all of which (when adult) swim along the sea floor on one side of the body, which is highly compressed and has both eyes on the uppermost side