le·​thal | \ ˈlē-thəl How to pronounce lethal (audio) \

Definition of lethal

 (Entry 1 of 2)

1a : of, relating to, or causing death death by lethal injection
b : capable of causing death lethal chemicals
2 : gravely damaging or destructive : devastating a lethal attack on his reputation
3 : very potent or effective a lethal fastball also : having a high alcohol content a lethal rum punch



Definition of lethal (Entry 2 of 2)

1 : an abnormality of genetic origin causing the death of the organism possessing it

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Other Words from lethal


lethality \ lē-​ˈtha-​lə-​tē How to pronounce lethality (audio) \ noun
lethally \ ˈlē-​thə-​lē How to pronounce lethally (audio) \ adverb

Synonyms & Antonyms for lethal

Synonyms: Adjective

baleful, deadly, deathly, fatal, fell, killer, mortal, murderous, pestilent, terminal, vital

Antonyms: Adjective

healthful, healthy, nonfatal, nonlethal, wholesome

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Choose the Right Synonym for lethal


deadly, mortal, fatal, lethal mean causing or capable of causing death. deadly applies to an established or very likely cause of death. a deadly disease mortal implies that death has occurred or is inevitable. a mortal wound fatal stresses the inevitability of what has in fact resulted in death or destruction. fatal consequences lethal applies to something that is bound to cause death or exists for the destruction of life. lethal gas

Examples of lethal in a Sentence


a potentially lethal dose of a drug He was sentenced to death by lethal injection.

Recent Examples on the Web: Adjective

Schwartz and Savage are using a twist on the Monster of the Week structure by regularly introducing characters and conflicts that only stick around for about three episodes before being resolved, typically in a lethal fashion. Samantha Nelson, The Verge, "Season 2 of Runaways forges a bold new path — eventually," 21 Dec. 2018 The bacteria make spores which help them survive; and, under certain conditions, the spores can grow and make one of the most lethal toxins known, the CDC explains. Korin Miller, SELF, "Del Monte Recalls Canned Corn Over Concerns It Could Cause ‘Life-Threatening Illness'," 14 Dec. 2018 It is made for the Gulf of Bothnia and the alleyways of Jokkmokk and the lethal zephyrs of Njörðr. Joseph O’neill, The New Yorker, "The First World," 21 June 2018 The amount of fentanyl seized this past year equals more than 24,000 lethal doses, according to the report. Rachel D'oro, The Seattle Times, "Report: Fentanyl deaths in Alaska quadrupled in 2017," 5 Sep. 2018 The Journal of Environmental Biology released a report in 1989 indicating that DEET could build up in the organs of freshwater fish over time, potentially accumulating to lethal doses. Wes Siler, Outside Online, "Is DEET Safe?," 18 May 2018 The two died from lethal doses of fentanyl, a drug that is at least 50 times stronger than heroin. Gary Fineout, OrlandoSentinel.com, "Florida, 5 other states sue opioid makers," 15 May 2018 Massive stars, which live short lives and then explode as incendiary supernovae, would deliver lethal doses of radiation to nearby planets, sterilizing any life that happened to exist—and leaving behind no observers. Adam Mann, Science | AAAS, "Dark energy’s weakness may be why supernovae didn’t kill us all," 4 May 2018 Radiation sensors inside the mannequin and on a second one without the vest are supposed to demonstrate the effectiveness of the material in protecting human organs from potentially lethal doses of high-energy radiation. Andy Pasztor, WSJ, "U.S., Israeli Space Agencies Join Forces to Protect Astronauts From Radiation," 17 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'lethal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of lethal


circa 1604, in the meaning defined at sense 1a


1917, in the meaning defined at sense 1

History and Etymology for lethal

Adjective and Noun

Latin letalis, lethalis, from letum death

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Statistics for lethal

Last Updated

4 Apr 2019

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Time Traveler for lethal

The first known use of lethal was circa 1604

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English Language Learners Definition of lethal

: causing or able to cause death


le·​thal | \ ˈlē-thəl How to pronounce lethal (audio) \

Medical Definition of lethal

 (Entry 1 of 2)

: of, relating to, or causing death a lethal injury also : capable of causing death lethal chemicals a lethal dose

Other Words from lethal

lethality \ lē-​ˈthal-​ət-​ē How to pronounce lethality (audio) \ noun, plural lethalities
lethally adverb



Medical Definition of lethal (Entry 2 of 2)

1 : an abnormality of genetic origin causing the death of the organism possessing it usually before maturity

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More from Merriam-Webster on lethal

Thesaurus: All synonyms and antonyms for lethal

Spanish Central: Translation of lethal

Nglish: Translation of lethal for Spanish Speakers

Britannica English: Translation of lethal for Arabic Speakers

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