may fish vs killifish

may fish and killifish both are nouns.

Word	Noun	Adjective	Verb	Adverb
may fish	Yes	No	No	No
killifish	Yes	No	No	No

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

may fish: black-barred fish of bays and coastal marshes of the Atlantic and Gulf Coast of the United States
killifish: small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control

may fish (noun)	killifish (noun)
black-barred fish of bays and coastal marshes of the Atlantic and Gulf Coast of the United States	small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control