1poetic, rare A firefly, a glow-worm.
2US The larva of any of several small moths of the superfamily Tortricoidea which are pests of the cranberry and other cultivated plants; especially (more fully "black-headed fireworm") the widespread Rhopobota naevana (also called holly tortrix).
So called because plants on which the larvae have fed may appear blackened as if by fire.
3Any of various predatory bristle worms (polychaetes) of the family Amphinomidae, having stinging bristles that can cause severe inflammation; especially (more fully "bearded fireworm") Hermodice carunculata of the tropical Atlantic, Caribbean, and Mediterranean.
4Any of several bristle worms (polychaetes) of the genus Odontosyllis (family Syllidae), which become bioluminescent during the mating period; especially (more fully "Bermuda fireworm") O. enopla of the tropical west Atlantic.
Mid 16th century (in an earlier sense). From fire + worm.