American flagfish vs killifish

American flagfish and killifish both are nouns.

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

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

American 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

American 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