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
-
in a manner resembling or suggesting death.
deadly pale.
-
excessively; completely.
deadly dull.
adjective
-
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.
Deadly encounters between humans and the animals are extremely rare.
From BBC • Apr. 23, 2026
Deadly flooding in Greece during intense rainfall in recent years has forced the authorities to improve floodworks to limit damage.
From Barron's • Jan. 22, 2026
Deadly force “shall not be used solely to prevent the escape of a fleeing subject.”
From Salon • Jan. 14, 2026
But on the battlefield, she and the rest of the Deadly Viper Assassination Squad are warriors first, women inconsequentially.
From Los Angeles Times • Dec. 5, 2025
The Cards of Deadly Fate are reporting a breach.
From "The Marvellers" by Dhonielle Clayton
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.
