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[lee-thuh l] /ˈli θəl/
of, relating to, or causing death; deadly; fatal:
a lethal weapon; a lethal dose.
made or carried out to cause death:
a lethal chamber; a lethal attack.
causing great harm or destruction:
The disclosures were lethal to his candidacy.
Origin of lethal
1575-85; < Latin lētālis, equivalent to lēt(um) death + -ālis -al1; spelling (hence pronunciation) with -h- by association with Greek lḗthē oblivion
Related forms
lethality, lethalness, noun
lethally, adverb
hyperlethal, adjective
nonlethal, adjective
nonlethally, adverb
semilethal, adjective
1. See fatal. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for lethal
Contemporary Examples
Historical Examples
  • Often in lethal strife of war Mavors, or swift Triton's queen, or the Rhamnusian virgin, in person did exhort armed bodies of men.

    The Carmina of Caius Valerius Catullus Caius Valerius Catullus
  • It was almost as if he had emerged from the lethal presence of the fumigator itself.

    The Market-Place Harold Frederic
  • He twisted the dial of the Stoltz to 'lethal' and to 'max area.'

    Evil Out of Onzar Mark Ganes
  • History is full of cruel tragedies caused by the lethal sex.

    Love Among the Chickens P. G. Wodehouse
  • If only he could burn them through and free himself and the professor before any of the pigmies re-entered that lethal chamber!

British Dictionary definitions for lethal


able to cause or causing death
of or suggestive of death
Derived Forms
lethality (liːˈθælɪtɪ) noun
lethally, adverb
Word Origin
C16: from Latin lēthālis, from lētum 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
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Word Origin and History for lethal

1580s, from Late Latin lethalis, alteration of Latin letalis "deadly, fatal," from letum "death," of uncertain origin. Form altered in Late Latin by association with lethe hydor "water of oblivion" in Hades in Greek mythology, from Greek lethe "forgetfulness."

Online Etymology Dictionary, © 2010 Douglas Harper
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lethal in Medicine

lethal le·thal (lē'thəl)

  1. Capable of causing death.

  2. Of, relating to, or causing death.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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