Source : Webster's Revised Unabridged Dictionary (1913)

Killifish \Kil"li*fish`\, n. (Zo["o]l.)
   Any one of several small American cyprinodont fishes of the
   genus {Fundulus} and allied genera. They live equally well in
   fresh and brackish water, or even in the sea. They are
   usually striped or barred with black. Called also {minnow},
   and {brook fish}. See {Minnow}.

Source : WordNet®

killifish
     n : small mostly marine warm-water carp-like schooling fishes;
         used as bait or aquarium fishes or in mosquito control
     [also: {killifishes} (pl)]