gadfly

Origin

From gad (“sharp point, spike; (dialectal) sharp-pointed rod for driving cattle, horses, etc., goad”) + fly, in the sense of a fly which irritates cattle, etc., by biting them, similar to the prodding of a goad. Gad is derived from Middle English gad, gadde (“metal spike with a sharp point; stick with a sharp point for driving animals, goad; metal bar or rod, ingot; (by extension) lump of material; metal rod for measuring land; (by extension) unit of linear measure equal to about 10 to 16 feet”), borrowed from Old Norse gaddr (“spike; goad”), from Proto-Germanic *gazdaz (“spike; goad”), further etymology uncertain. Displaced native Old English bēaw. Sense 2.1.1 (“person who upsets the status quo”) may allude to the Apology by the Greek philosopher Plato (428/427 or 424/423 - 348/347 B.C.E.), where he describes Socrates (c. 470 - 399 B.C.E.) acting as a goad to the Athenian political scene like a gadfly (Ancient Greek μῠ́ωψ (mŭ́ōps)) arousing a sluggish horse.