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.

late 15c. (Caxton), "infest with disease or other natural calamity," from Middle Dutch plaghen, from plaghe (n.) "plague" (see plague (n.)). The sense of "vex, harass, bother, annoy" is recorded from 1590s. Related: Plagued; plaguing.

1570s, "pertaining to a plague," from plague (n.) + -y (2). Figurative meaning "vexatious, troublesome" is from 1610s. As an adverb, "vexatiously, deucedly" (properly plaguily) it is attested from 1580s, often with deliberate attempt at humor. Johnson also has woundy "excessive." The sense of "plague-stricken, marked by the plague" (c. 1600) is now archaic or obsolete.

"sudden fit of paralysis and dizziness," late 14c., from Old French apoplexie or directly from Late Latin apoplexia, from Greek apoplexia, from apoplektos "disabled by a stroke, struck dumb," verbal adjective from apoplēssein "to strike down and incapacitate," from apo "off" (see apo-), in this case perhaps an intensive prefix, + plēssein "to hit" (from PIE root *plak- (2) "to strike;" source also of plague, which also has a root sense of "stricken"). The Latin translation, sideratio, means "disease caused by a constellation."

*plāk-, Proto-Indo-European root meaning "to strike."

It forms all or part of: apoplexy; cataplexy; complain; fling; paraplegia; plaint; plangent; plankton; planxty; plague; plectrum; quadriplegia.

It is the hypothetical source of/evidence for its existence is provided by: Greek plazein "to drive away," plēssein "to beat, strike;" Latin plangere "to strike, lament;" Old English flocan "to strike, beat;" Gothic flokan "to bewail;" German fluchen, Old Frisian floka "to curse."

mid-15c., pestiferus, "bringing plague, plague-bearing, pestilential," also in a weakened or figurative sense, "mischievous, malignant, pernicious, hurtful to morals or society," from of Latin pestiferus "that brings plague or destruction," variant of pestifer "bringing plague, destructive, noxious," from pestis "plague" (see pest) + ferre "carry," from PIE root *bher- (1) "to carry," also "to bear children." Related: Pestiferously; pestiferousness.

c. 1300, "any infectious or contagious disease, fatal epidemic," from Old French pestilence "plague, epidemic" (12c.) and directly from Latin pestilentia "a plague, an unwholesome atmosphere," noun of condition from pestilentem (nominative pestilens) "infected, unwholesome, noxious," from pestis "deadly disease, plague" (see pest).

Also in Middle English "wickedness, evil, sin, a vice, that which is morally pestilential."

late 14c., pestilencial, "producing or tending to produce an infectious disease, characterized by the plague," from Medieval Latin pestilentialis, from Latin pestilentia "plague" (see pestilence). Weakened sense of "mischievous, pernicious" is from 1530s. Related: Pestilentially.