Definitions
1.nounAny dipterous insect of the family Oestridae, commonly known as botflies.
2.nounA horsefly: any of various species of fly, of the family Tabanidae, noted for buzzing about animals and sucking their blood.
3.nounOne who upsets the status quo by posing upsetting or novel questions, or attempts to stimulate innovation by proving an irritant.
4.nounOne who merely irritates without making useful suggestions.
5.nounA bloodsucker; a person who takes without giving back."He's a regular gadfly and takes advantage of his friend's generosity."