1550s (in imprecations, "a pest upon ____," etc.), "plague, pestilence, epidemic disease," from French peste (1530s), from Latin pestis "deadly contagious disease; a curse, bane," a word of uncertain origin. Meaning "any noxious, destructive, or troublesome person or thing" is attested by c. 1600. Pest-house "hospital for persons suffering from infectious diseases" is from 1610s.
"troublesome, annoying," 1775, originally in New England dialect, perhaps a dialectal formation from pest (OED compares plaguy "confounded, annoying, disagreeable"). Partridge suggests an origin in Essex dialect. Sometimes in American-English colloquial use a mere intensive, "excessively." Related: Peskily.
late 14c., "contaminated with dangerous disease; deadly, poisonous," from Latin pestilentem (nominative pestilens) "infected, unhealthy," from pestilis "of the nature of a plague," from pestis "deadly contagious disease" (see pest (n.)). Transferred sense of "mischievous, pernicious, hurtful to health or morals" is from 1510s; weakened sense of "troublesome" is from 1590s. Related: Pestilently.
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."
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.
1520s, "to clog, entangle, encumber" (a sense now obsolete), probably a shortening of empester, impester, from French empestrer "place in an embarrassing situation" (Modern French empêtrer, Walloon epasturer), from Vulgar Latin *impastoriare "to hobble" (an animal), from Latin im- "in" + Medieval Latin pastoria (chorda) "(rope) to hobble an animal," from Latin pastoria, fem. of pastorius "of a herdsman," from pastor "herdsman" (see pastor (n.)).
Or directly from the French word. The sense of "annoy, disturb, trouble" (1560s) is from influence of pest. Related: Pestered; pestering.