Definition of gadfly noun from the Oxford Advanced American Dictionary

 

gadfly

 noun
noun
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 The billionaire political gadfly says he is running for president.
See the Oxford Advanced Learner's Dictionary entry: gadfly