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
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 force is authorized only when an officer believes there’s an “imminent threat of death or serious bodily injury” and there is “no alternative.”
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
Deadly fires were once a regular scourge in densely populated Hong Kong, especially in poorer neighbourhoods, but improved safety measures have made them far less common.
From Barron's • Nov. 27, 2025
Deadly storm surge and damaging winds are expected starting late Tuesday.
From The Wall Street Journal • Oct. 27, 2025
My sources say that there was a piece of evidence that’s gone missing from the reports about the breach of the Cards of Deadly Fate.
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.
