butterfish vs percoid

butterfish and percoid both are nouns.

Word	Noun	Adjective	Verb	Adverb
butterfish	Yes	No	No	No
percoid	Yes	No	No	No

As nouns, percoid is a hypernym of butterfish; that is, percoid is a word with a broader meaning than butterfish:

butterfish: small marine fish with a short compressed body and feeble spines
percoid: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of butterfish include percoid fish, percoidean.

butterfish (noun)	percoid (noun)
small marine fish with a short compressed body and feeble spines	any of numerous spiny-finned fishes of the order Perciformes
slippery scaleless food fish of the northern Atlantic coastal waters
any of numerous small flat Atlantic food fish having smooth skin