deadly
Americanadjective
-
deadlier,
comparative
-
deadliest
superlative
-
causing or tending to cause death; fatal; lethal.
a deadly poison.
-
aiming to kill or destroy; implacable.
a deadly enemy.
-
like death.
a deadly pallor.
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excruciatingly boring.
The dinner party was absolutely deadly.
-
deadly haste.
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extremely accurate.
Annie Oakley was a deadly shot.
adverb
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in a manner resembling or suggesting death.
deadly pale.
-
excessively; completely.
deadly dull.
adjective
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likely to cause death
deadly poison
deadly combat
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informal extremely boring
adverb
Synonym Usage
See fatal.
Other Word Forms
Derived Forms
Inflected Forms
Adjectives
Etymology
Origin of deadly
First recorded before 900; Middle English deedli(ch), Old English dēadlīce; see dead, -ly
Explanation
Something that's deadly can kill you. Because a gun can end someone's life, it's a deadly weapon. If someone's diagnosed with a deadly disease, it's lethal — it's capable of ending the person's life. When you hear someone talk about police officers using "deadly force," they mean actions that intended to cause death, or understood to be capable of killing someone. You can also use the word to mean "extremely" or "very," as when you describe your math class as deadly boring.
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
French President Emmanuel Macron on Saturday announced Paris would deliver new interceptor missiles to Ukraine, with Kyiv's air defences running short after the latest round of deadly Russian attacks.
From Barron's ● Aug. 22, 2026
Out-of-service utility infrastructure managed by Southern California Edison started the deadly conflagration in January 2025 that killed 19 people and destroyed much of Altadena, according to firefighters’ official investigation.
From Los Angeles Times ● Aug. 20, 2026
Experts believe that midges infected with the potentially deadly disease were blown over the border from England, where there are currently 439 cases, external.
From BBC ● Aug. 17, 2026
Prosecutors say Mr. Mangione wrote in a notebook that he was rebelling against “the deadly, greed fueled health insurance cartel.”
From The Wall Street Journal ● Aug. 16, 2026
As far as the two-spheres theory was concerned, the voyages of Vespucci were deadly.
From "The Invention of Science" by David Wootton
Bacterial meningitis, as seen in this outbreak, is rarer and deadlier than the viral type.
From Barron's ● Mar. 19, 2026
A 2024 study in Nature shows that while EVs reduced nitrogen-oxide emissions—a precursor to smog—by 1% since 2020, they have increased far deadlier sulfur-dioxide and particulate-matter pollution by 10% and 20%, respectively.
From The Wall Street Journal ● Nov. 10, 2025
Only dioxins, which come primarily from burning waste materials, are deadlier than airborne hexavalent chromium.
From Los Angeles Times ● Oct. 13, 2025
So far, most of the cases of the deadlier strain, known as clade Ib, have been on the African content, especially in the Democratic Republic of Congo.
From Salon ● Aug. 22, 2024
It was a stupid comparison, anyway—hollowgast were scarier, and probably deadlier, than any movie monster.
From "Hollow City" by Ransom Riggs
A 2023 American Civil Liberties Union report found that of the 10 deadliest school shootings in two decades, eight happened on campuses that already had surveillance cameras.
From Slate ● Aug. 21, 2026
The Boxing Day tragedy was one of the deadliest natural disasters in recorded history.
From Barron's ● Aug. 15, 2026
The deadliest aspect of fires has declined, too: smoke deaths.
From The Wall Street Journal ● Aug. 12, 2026
It also found that 2025 was the deadliest year for Jews in the diaspora in more than three decades.
From BBC ● Aug. 5, 2026
The sides were set for the biggest and deadliest war in history—the United States, Great Britain, and the Soviet Union led the Allied Powers against the Axis Powers of Germany, Japan, and Italy.
From "Bomb" by Steve Sheinkin
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
