Definition from Wiktionary, the free dictionary
gadfly (plural gadflies)
- Any dipterous insect of the family Oestridae, commonly known as botflies.
- A horsefly: any of various species of fly, of the family Tabanidae, noted for buzzing about animals and sucking their blood.
- One who upsets the status quo by posing upsetting or novel questions, or attempts to stimulate innovation by proving an irritant.
- (pejorative) One who merely irritates without making useful suggestions.
- (slang) A bloodsucker
- He's a regular gadfly and takes advantage of his friend's generosity.
fly of the family Oestridae — see botfly
fly of the family Tabanidae — see horsefly
one who upsets the status quo
one who merely irritates