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  1. causing insidious harm or ruin; ruinous; injurious; hurtful: pernicious teachings; a pernicious lie.
  2. deadly; fatal: a pernicious disease.
  3. Obsolete. evil; wicked.
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Origin of pernicious

1515–25; < Latin perniciōsus ruinous, equivalent to pernici(ēs) ruin (per- per- + -nici-, combining form of nex death, murder (stem nec-) + -iēs noun suffix) + -ōsus -ous
Related formsper·ni·cious·ly, adverbper·ni·cious·ness, nounun·per·ni·cious, adjectiveun·per·ni·cious·ly, adverb

Synonyms for pernicious

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for pernicious

devastating, noxious, deadly, poisonous, virulent, malicious, harmful, toxic, nefarious, detrimental, dangerous, lethal, ruinous, destructive, damaging, baleful, deleterious, evil, fatal, iniquitous

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Historical Examples of pernicious

British Dictionary definitions for pernicious


  1. wicked or maliciouspernicious lies
  2. causing grave harm; deadly
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Derived Formsperniciously, adverbperniciousness, noun

Word Origin for pernicious

C16: from Latin perniciōsus, from perniciēs ruin, from per- (intensive) + nex death
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for pernicious


early 15c., from Middle French pernicios (13c., Modern French pernicieux) and directly from Latin perniciosus "destructive," from pernicies "destruction, death, ruin," from per- "completely" (see per) + necis "violent death, murder," related to necare "to kill," nocere "to hurt, injure, harm," noxa "harm, injury" (see noxious). Related: Perniciously; perniciousness.

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Online Etymology Dictionary, © 2010 Douglas Harper

pernicious in Medicine


  1. Tending to cause death or serious injury; deadly.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.