deadly
Americanadjective
-
causing or tending to cause death; fatal; lethal.
a deadly poison.
-
aiming to kill or destroy; implacable.
a deadly enemy.
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like death.
a deadly pallor.
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excruciatingly boring.
The dinner party was absolutely deadly.
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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
Related Words
See fatal.
Other Word 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 American national and a French woman evacuated from the cruise ship hit by a deadly hantavirus outbreak have tested positive, officials said Monday, as the complex operation to repatriate those on board continued.
From Barron's • May 11, 2026
It might be a joke, but it can be deadly serious, too.
From Salon • May 10, 2026
The deadly fires that devastated homes in Pacific Palisades and Altadena also laid waste to a lush canopy of leaves and pine needles that had cooled and shaded residents here for generations.
From Los Angeles Times • May 7, 2026
The crisis - triggered after a deadly militant attack on tourists in Indian-administered Kashmir, and culminating in military strikes by India and retaliatory action from Pakistan - lasted barely 90 hours.
From BBC • May 7, 2026
Ma trains that deadly, all-too-familiar gaze on me.
From "Kwame Crashes the Underworld" by Craig Kofi Farmer
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.
