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.
-
excruciatingly boring.
The dinner party was absolutely deadly.
-
deadly haste.
-
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
-
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:
More than 4,000 people have died from Ebola in DR Congo this year, in what is the second most deadly known outbreak of the disease.
From BBC ● Oct. 6, 2026
All three victims of the deadly medical helicopter crash off Catalina Island have been publicly identified.
From Los Angeles Times ● Oct. 3, 2026
Her condition Thursday was not known, and Tennessee officials have not said how she survived the deadly doses of pentobarbital.
From Barron's ● Oct. 1, 2026
The deadly clashes seem anticlimactic, as the subtitle foretells who vanquished whom.
From The Wall Street Journal ● Sep. 28, 2026
The Supreme Court dismissed the case, however, ruling that Lyons lacked “standing” to seek an injunction against the deadly practice.
From "The New Jim Crow" by Michelle Alexander
Meanwhile, real-time satellite intel is making Kyiv’s drone strikes deadlier than ever.
From The Wall Street Journal ● Jun. 5, 2026
He said a security guard at the Islamic center was among the three victims killed and his response had helped prevent a deadlier attack.
From Barron's ● May 18, 2026
Through these mutations, they can become more contagious, evade immunity, and become deadlier.
From Salon ● Nov. 28, 2025
Only dioxins, which come primarily from burning waste materials, are deadlier than airborne hexavalent chromium.
From Los Angeles Times ● Oct. 13, 2025
It was a stupid comparison, anyway—hollowgast were scarier, and probably deadlier, than any movie monster.
From "Hollow City" by Ransom Riggs
The accident is one of the deadliest air disasters in Nigeria in recent years.
From BBC ● Oct. 6, 2026
The 21-mile stretch of PCH that runs through Malibu is one of the deadliest and most notorious roads in the state, with an average of about four crash-related fatalities per year over the last decade.
From Los Angeles Times ● Oct. 5, 2026
Global Witness says that 85% of the documented killings took place in Latin America, making it the deadliest region for every year since the group started publishing its reports in 2012.
From BBC ● Sep. 16, 2026
The 27-year-old from Moscow, who switched allegiance to Kazakhstan in 2018 in search of greater support, is the deadliest server on the women’s circuit.
From The Wall Street Journal ● Sep. 12, 2026
The Spanish flu of 1918 had raged through the continent, killing nearly 20 million men and women worldwide and ranking among the deadliest natural disasters in history.
From "The Gene" by Siddhartha Mukherjee
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.
