Definition of gadfly noun from the Oxford Advanced Learner's Dictionary

 

gadfly

 noun
noun
BrE BrE//ˈɡædflaɪ//
 
; NAmE NAmE//ˈɡædflaɪ//
 
(pl. gadflies)(usually disapproving)
 
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a person who annoys or criticizes other people in order to make them do something He was a political gadfly, turning up at city council meetings and complaining about the waste of taxpayers’ money. Word Origin late 16th cent.: from gad, or obsolete gad ‘goad, spike’, from Old Norse gaddr, of Germanic origin; related to yard, the unit of measurement.
See the Oxford Advanced American Dictionary entry: gadfly