deadly
Americanadjective
-
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
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.
An ATF agent testified Jonathan Rinderknecht was dealing with major anxiety and anger issues when he allegedly caused a fire in 2025 that later reignited as the destructive and deadly Palisades blaze.
From Los Angeles Times • Jun. 12, 2026
Texas rancher Stephen Diebel spent 18 months tracking a deadly, long-eradicated parasite as it inched its way back toward the U.S. border.
From The Wall Street Journal • Jun. 12, 2026
"An El Niño declaration is not just another weather forecast - for millions of people it is a deadly siren to be feared," said Mohamed Adow, director of campaign group Power Shift Africa.
From BBC • Jun. 11, 2026
He has completed two missions aboard the International Space Station and carried out complex spacewalks, including one that could have turned deadly when his helmet began filling with water.
From Barron's • Jun. 9, 2026
Zheng was making outraged gestures as if he were deadly serious.
From "The Boy Who Met a Whale" by Nizrana Farook
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.
