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).
c. 1300, scourgen, "to whip, flog" (another, one's self or body, an animal), from Old French escorgier "to whip" and in part from scourge (n.). The figurative meaning "afflict severely, chastise" (often for the sake of punishment or purification) is from late 14c., Biblical. Essentially a doublet of excoriate. Related: Scourged; scourging.
For whom the Lord loveth he chasteneth,
And scourgeth every son whom he receiveth.
[Hebrews xii.6, KJV]
early 15c., "the scourging of Christ," from Old French flagellacion "scourging, flogging," or directly from Latin flagellationem (nominative flagellatio) "a scourging," noun of action from past-participle stem of flagellare "to scourge, lash" (see flagellum). In a general sense from 1520s.
"long, lash-like appendage," 1837, from Latin flagellum "whip, scourge," also figurative, diminutive of flagrum "a whip," from PIE root *bhlag- "to strike" (source also of Latin flagitium "shameful act, passionate deed, disgraceful thing," flagitare "to demand importunately;" Old Norse blakra "to flutter with the wings," blekkja "to impose upon;" Lithuanian blaškau,blaškyti "to and fro").
late 14c., plage, "affliction, calamity, evil, scourge, severe trouble or vexation;" early 15c., "malignant disease," from Old French plage (14c., Modern French plaie), from Late Latin plaga "affliction; slaughter, destruction," used in Vulgate for "pestilence," from Latin plaga "stroke, wound," probably from root of plangere "to strike, lament (by beating the breast)," from or cognate with Greek (Doric) plaga "blow" (from PIE root *plak- (2) "to strike").
Sometimes in Middle English also "a strike, a blow" (late 14c.). The Latin word also is the source of Old Irish plag (genitive plaige) "plague, pestilence," German Plage, Dutch plaage. Meaning "epidemic that causes many deaths" is from 1540s; specifically in reference to bubonic plague from c. 1600. Modern spelling follows French, which had plague from 15c. Weakened sense of "anything annoying" is from c. 1600.