gadfly |ˈɡadˌflī| noun (plural gadflies)
- An annoying person, especially one who provokes others into action by criticism.
- A fly that bites livestock, especially a horsefly, warble fly, or botfly.
ORIGIN late 16th century: from gad1, or obsolete gad ‘goad, spike,’ from Old Norse gaddr, of Germanic origin; related to yard1.