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.
This organism can cause a rare but extremely deadly brain infection when contaminated water enters the nose, often during swimming or other recreational water activities.
From Science Daily • Jun. 6, 2026
Erickson, 58, was in a separate AMG Mercedes SUV ahead of Grossman’s vehicle and was also found negligent in the deadly crash.
From Los Angeles Times • Jun. 6, 2026
Today, Kelver, a 28-year-old trans woman, faces two felony charges—aggravated assault and possession of a deadly weapon with unlawful intent—which could carry up to 15 years in prison.
From Slate • Jun. 4, 2026
The virus, which can cause a deadly haemorrhagic fever, has been detected in three Congolese provinces as well as in Uganda.
From Barron's • May 31, 2026
Lightning filled the sky like a sudden flash of deadly sunlight.
From "Worth" by A. LaFaye
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.
