oilfish vs gempylid

oilfish and gempylid both are nouns.

Word	Noun	Adjective	Verb	Adverb
oilfish	Yes	No	No	No
gempylid	Yes	No	No	No

As nouns, gempylid is a hypernym of oilfish; that is, gempylid is a word with a broader meaning than oilfish:

oilfish: very large deep-water snake mackerel
gempylid: snake mackerels; elongated marine fishes with oily flesh; resembles mackerels; found worldwide

oilfish (noun)	gempylid (noun)
very large deep-water snake mackerel	snake mackerels; elongated marine fishes with oily flesh; resembles mackerels; found worldwide