plague (n.)

*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."

"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."

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.