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.
The country has been battered by monsoon rains since Sunday, with several deadly landslides reported in Cox's Bazar.
From BBC • Jul. 8, 2026
The shortage has left its capital, Kyiv, and other cities exposed during deadly large-scale Russian attacks this summer.
From The Wall Street Journal • Jul. 8, 2026
A growing number of deadly West Nile virus-carrying mosquitoes are spreading rapidly across Southern California and local officials are urging residents to take action to ward off a bite.
From Los Angeles Times • Jul. 8, 2026
Davies said: "The lives of babies are at risk because these platforms won't stop dangerous products from reaching their customers - even though they are well aware that these products can be deadly."
From BBC • Jul. 8, 2026
“Sit back down immediately, and wait five minutes,” Aunt Kitty directed, her voice deadly.
From "The Detective's Assistant" by Kate Hannigan
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.
