butterfish vs gunnel

butterfish and gunnel both are nouns.

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

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

butterfish: slippery scaleless food fish of the northern Atlantic coastal waters
gunnel: small eellike fishes common in shallow waters of the northern Atlantic

Other hypernyms of butterfish include bracketed blenny.

butterfish (noun)	gunnel (noun)
small marine fish with a short compressed body and feeble spines	small eellike fishes common in shallow waters of the northern Atlantic
slippery scaleless food fish of the northern Atlantic coastal waters	wale at the top of the side of boat; topmost planking of a wooden vessel
any of numerous small flat Atlantic food fish having smooth skin