noun any fly resembling a culex in form or habits; ·esp., in america, a small biting fly of the genus simulium and allies, as the buffalo gnat, the black fly, ·etc.
2. gnat ·noun a blood-sucking dipterous fly, of the genus culex, undergoing a metamorphosis in water. the females have a proboscis armed with needlelike organs for penetrating the skin of animals. these are wanting in the males. in america they are generally called mosquitoes. ·see mosquito.