gadfly — ONAD

gadfly /ˈɡadˌflī, ˈɡædˌflaɪ

▸ noun

(plural gadflies)

a fly that bites livestock, especially a horsefly, warble fly, or botfly.

▪ an annoying person, especially one who provokes others into action by criticism:

always a gadfly, he attacked intellectual orthodoxies.

– ORIGIN late 16th century : from gad, or obsolete gad ‘goad, spike’, from Old Norse gaddr, of Germanic origin; related to yard1.