warn
Americanverb (used with object)
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to give notice, advice, or intimation to (a person, group, etc.) of danger, impending evil, possible harm, or anything else unfavorable.
They warned him of a plot against him. She was warned that her life was in danger.
- Synonyms:
- forewarn
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to urge or advise to be careful; caution.
to warn a careless driver.
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to admonish or exhort, as to action or conduct.
She warned her employees to be on time.
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to notify, advise, or inform.
to warn a person of an intended visit.
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to give notice to (a person, group, etc.) to go, keep at a distance, etc. (often followed by away, off, etc.).
A sign warns trespassers off the grounds. A marker warned boats away from the dock.
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to give authoritative or formal notice to (someone); order; summon.
to warn a person to appear in court.
verb (used without object)
verb
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to notify or make (someone) aware of danger, harm, etc
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(tr; often takes a negative and an infinitive) to advise or admonish (someone) as to action, conduct, etc
I warn you not to do that again
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(takes a clause as object or an infinitive) to inform (someone) in advance
he warned them that he would arrive late
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(tr; usually foll by away, off, etc) to give notice to go away, be off, etc
he warned the trespassers off his ground
Synonym Usage
Warn, caution, admonish imply attempting to prevent another from running into danger or getting into unpleasant or undesirable circumstances. To warn is to speak plainly and usually in strong terms: to warn him about danger and possible penalties. To caution is to advise about necessary precautions, to put one on one's guard about possibly harmful circumstances or conditions, thus emphasizing avoidance of undesirable consequences: to caution him against driving in such weather. Admonish suggests giving earnest, authoritative advice with only tacit references to danger or penalty: to admonish a person for neglecting his duties.
Other Word Forms
Derived Forms
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warnernoun
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prewarnverb (used with object)
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rewarnverb (used with object)
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unwarnedadjective
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well-warnedadjective
Inflected Forms
Participles
Conjugated Forms
Present
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warnsimple
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warnssimple
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have warnedperfect
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has warnedperfect
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am warningprogressive
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are warningprogressive
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is warningprogressive
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have been warningperfect progressive
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has been warningperfect progressive
Past
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warnedsimple
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had warnedperfect
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was warningprogressive
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were warningprogressive
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had been warningperfect progressive
Future
Etymology
Origin of warn
First recorded before 1000; Middle English warnen, Old English warnian; cognate with German warnen; Cf. ware 2
Explanation
When you warn someone, you advise them to be careful or tell them about a problem or danger. If you perform a dangerous stunt, you should probably warn your audience, "Don't try this at home." Many traffic signs are meant to warn drivers about hazards, like bridges that get slippery in the rain or bumps in the road. And the purpose of a dog's growl is to warn another dog (or human) that it's stressed or fearful. A warning is a helpful message, no matter what form it comes in, and to warn is to send this message. The Old English root is warnian, "give notice of impending danger."
Vocabulary lists containing warn
"The Secret Water"
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"The Black Ferris" by Ray Bradbury
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Tasting the Sky
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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:
On Monday, the stock had closed below the 200-DMA, a widely followed long-term trend tracker, for the first time in a year, to warn that a downtrend may have started.
From MarketWatch ● Jul. 21, 2026
While some tech professionals embrace the productivity benefits of constant recording, others warn the practice could stifle conversation.
From The Wall Street Journal ● Jul. 17, 2026
But experts warn the sprawling salt flats of Montenegro's Ulcinj salina, a vital stop-off for migrating flamingos, pelicans and other species, is fading fast.
From Barron's ● Jul. 15, 2026
The high temperatures come not long after a record-breaking 4 July heatwave hit large portions of the US, leading experts to warn people to exercise caution.
From BBC ● Jul. 14, 2026
“I’ve got to warn Alex!” said Nim, and dialed the number.
From "Nim’s Island" by Wendy Orr
A “generational bear market” is looming for investors with little powder to take advantage of, as they have chased rising popular stocks, warns one veteran wealth manager.
From MarketWatch ● Jul. 17, 2026
Fencing exists along the aqueduct and MWD facilities “to prevent unauthorized access,” and signage warns about the dangers of entering the canal.
From Los Angeles Times ● Jul. 16, 2026
Instead, he warns, the technologies society is building could introduce significant new risks.
From Science Daily ● Jul. 14, 2026
The Nobel laureate, dubbed the “godfather of AI” for his work on artificial neural networks, warns of a 10% to 20% chance AI will wipe out humans.
From The Wall Street Journal ● Jul. 12, 2026
“Eventually,” warns Tom Hombein, thirty-three years after his ascent of the West Ridge, “what happened on Everest this season is certain to happen again.”
From "Into Thin Air" by Jon Krakauer
Prominent economists, tech leaders and researchers have warned that AI could transform the economy for better or worse, bringing large-scale job displacement.
From Los Angeles Times ● Jul. 22, 2026
More than a decade ago, Congress’s investigative arm warned that some insiders might have been amassing more in IRAs than the contribution limits allowed by using artificially low share prices to value startup holdings.
From The Wall Street Journal ● Jul. 22, 2026
The situation's so serious it's recently led to limits on house building, while campaigners have warned of "ecological disaster".
From BBC ● Jul. 22, 2026
Forecasters have warned of extreme heat this summer, with the Japan Meteorological Agency trying to raise public awareness by announcing the word "kokusho-bi", which means "brutally hot day" when the mercury exceeds 40C.
From BBC ● Jul. 21, 2026
Across the president’s desk in the Oval Office, Eisenhower warned Kennedy of the many Cold War challenges ahead.
From "Fallout: Spies, Superbombs, and the Ultimate Cold War Showdown" by Steve Sheinkin
The Los Angeles County Department of Public Health issued an extreme heat warning for residents of many areas, citing both daytime temperatures and unusually warm overnight conditions.
From Los Angeles Times ● Jul. 22, 2026
Anthropic and its chief executive, Dario Amodei, have been critical of that approach, warning that increased government intervention is needed to prevent AI-enabled catastrophe.
From The Wall Street Journal ● Jul. 22, 2026
The paper says senior economists are warning that the new prime minister will need to raise taxes, or else risk failing to deliver on his raft of "bolder policy pledges".
From BBC ● Jul. 22, 2026
"Tropical storm conditions will continue spreading across portions of the warning area later today through Wednesday," the NHC's latest advisory said.
From Barron's ● Jul. 21, 2026
When it's too dry or mixed in the wrong formula, almost anything can set it off, without warning.
From "Phineas Gage" by John Fleischman
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.