flagfish vs killifish

flagfish and killifish both are nouns.

Word	Noun	Adjective	Verb	Adverb
flagfish	Yes	No	No	No
killifish	Yes	No	No	No

As nouns, killifish is a hypernym of flagfish; that is, killifish is a word with a broader meaning than flagfish:

flagfish: a fish with a dark-blue back and whitish sides with red stripes; found in swamps and streams of Florida
killifish: small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control

flagfish (noun)	killifish (noun)
a fish with a dark-blue back and whitish sides with red stripes; found in swamps and streams of Florida	small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control