order Pleuronectiformes vs flatfish

order Pleuronectiformes and flatfish both are nouns.

Word	Noun	Adjective	Verb	Adverb
order Pleuronectiformes	Yes	No	No	No
flatfish	Yes	No	No	No

order Pleuronectiformes (noun)	flatfish (noun)
flatfishes: halibut; sole; flounder; plaice; turbot; tonguefishes	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 side
	sweet lean whitish flesh of any of numerous thin-bodied fish; usually served as thin fillets