c. 1200, "a whip used for inflicting pain or punishment, a lash used for torture," from Anglo-French scorge, escorge, back-formation from Old French scurge, eschurge "a whip, scourge, thong," from escorgier "to whip," which is from Vulgar Latin *excorrigiare. This is a compound of Latin ex- "out, off," or here perhaps intensive, (see ex-) + corrigia "thong, shoelace," in Late Latin "rein," with sense extension here to "whip." This is probably [Barnhart] from a Gaulish word related to Old Irish cuimrech "fetter," from PIE root *reig- "to bind" (see rig (v.)).
Figurative use is from late 14c., biblical, "a punishment, a punitive infliction;" also "one who or that which scourges or destroys." Scourge of God (Latin flagellum Dei), a title given by later generations to Attila the Hun (406-453 C.E.), is attested from late 14c. (Goddes scourge).