gunnel vs butterfish

gunnel and butterfish both are nouns.

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

As nouns, butterfish is a hyponym of gunnel; that is, butterfish is a word with a more specific, narrower meaning than gunnel:

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

Other hyponyms of gunnel include Pholis gunnellus, rock gunnel.

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