gadfly

US /ˈɡæd.flaɪ/
UK /ˈɡæd.flaɪ/
"gadfly" picture
1.

a person who annoys or provokes others with criticism, questions, or new ideas

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He was known as a political gadfly, constantly challenging the status quo.
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The professor acted as a gadfly, encouraging students to think critically.
:
agitatorprovocateurcritictroublemakernuisance
2.

a fly that bites livestock, especially a horsefly

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The horses were bothered by the persistent gadflies.
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A single gadfly can cause a lot of irritation to an animal.
:
horseflybotfly