gnat Meaning, Definition & Usage

  1. noun any of various small biting flies: midges; biting midges; black flies; sand flies
  2. noun (British usage) mosquito

WordNet

Gnat noun
Etymology
AS. gnæt.
Definitions
  1. (Zoöl.) 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.
  2. 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.

Webster 1913