deadly
Americanadjective
-
deadlier,
comparative
-
deadliest
superlative
-
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.
See Examples For:
Ebola is a rare but deadly viral disease and the Bundibugyo species is even rarer, with only two known prior outbreaks.
From BBC ● Aug. 17, 2026
The magazine also featured photographs of Macron engaging in water sports such as foil surfing, during a summer marked by successive heatwaves and deadly fires in France.
From Barron's ● Aug. 14, 2026
Some U.S. military officers, though, argue that drones are particularly deadly in this war because it has reached a stalemate with little battlefield movement.
From The Wall Street Journal ● Aug. 12, 2026
Latino men who cut artificial-stone countertops in California are falling ill from an incurable and deadly lung disease at an alarming rate, a new study finds.
From Los Angeles Times ● Aug. 12, 2026
A November stillness was settling like a deadly oxymoron on the April landscape.
From "The Secret History" by Donna Tartt
Bacterial meningitis, as seen in this outbreak, is rarer and deadlier than the viral type.
From Barron's ● Mar. 19, 2026
While about 500,000 people a year die from excessive heat, he says, “surprisingly, excessive cold is far deadlier, killing nearly ten times more.”
From The Wall Street Journal ● Oct. 30, 2025
Only dioxins, which come primarily from burning waste materials, are deadlier than airborne hexavalent chromium.
From Los Angeles Times ● Oct. 13, 2025
An outbreak in 2018-20 was far deadlier, claiming more than 2,000 lives.
From BBC ● Sep. 4, 2025
For one reason or another, the virus became a lot deadlier.
From "The Tipping Point" by Malcolm Gladwell
It is the country's deadliest earthquake since 2022, when hundreds of people were killed in West Java.
From BBC ● Aug. 17, 2026
It was one of the deadliest natural disasters in recorded history.
From Barron's ● Aug. 17, 2026
The deadliest aspect of fires has declined, too: smoke deaths.
From The Wall Street Journal ● Aug. 12, 2026
It also found that 2025 was the deadliest year for Jews in the diaspora in more than three decades.
From BBC ● Aug. 5, 2026
For sometimes, when we take the deadliest aim, we are nothing if not reckless.
From "Aru Shah and the End of Time" by Roshani Chokshi
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.
