Synonyms

warn

American

[wawrn] / wɔrn /

verb (used with object)

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
to urge or advise to be careful; caution.

to warn a careless driver.
to admonish or exhort, as to action or conduct.

She warned her employees to be on time.
to notify, advise, or inform.

to warn a person of an intended visit.
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.
to give authoritative or formal notice to (someone); order; summon.

to warn a person to appear in court.

verb (used without object)

to give a warning; caution.

to warn of further disasters.

warn British

/ wɔːn /

verb

to notify or make (someone) aware of danger, harm, etc
(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
(takes a clause as object or an infinitive) to inform (someone) in advance

he warned them that he would arrive late
(tr; usually foll by away, off, etc) to give notice to go away, be off, etc

he warned the trespassers off his ground

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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

Inflected Forms

Participles

Conjugated Forms

Present

Past

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."

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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:

warn warns warned warning

On Friday evening the UK's mobile phone alert system was used to warn people not to light anything which could spark a wildfire, including barbecues and garden incinerators.

From BBC ● Aug. 15, 2026

Some critics of the policy warn that airlines could misuse this freedom to entice customers with low base fares and high fees.

From Los Angeles Times ● Aug. 14, 2026

In a world where influencers warn of spiked cortisol levels and disrupted circadian rhythms, plenty of consumers are turning to prebiotic sodas, sugar-free beverages, and refreshers as substitutes.

From Slate ● Aug. 14, 2026

Mr. Carlson was trying to warn the president against military action.

From The Wall Street Journal ● Aug. 13, 2026

I don’t know what this woman is trying to warn me against, but something tells me that jumping into the water means a little more than just jumping into the water.

From "Kwame Crashes the Underworld" by Craig Kofi Farmer

Few voices call for absolute isolation, not when the United Nations warns that 22 million Afghans – nearly half the of the population – rely on some form of foreign assistance to help them survive.

From BBC ● Aug. 14, 2026

New research warns that prolonged periods of unusually warm ocean temperatures can also threaten human physical and mental health.

From Science Daily ● Aug. 11, 2026

The CDC warns that electric fans can actually raise your body temperature in extreme heat.

From Los Angeles Times ● Aug. 11, 2026

Handling wild game can pose food-safety risks: The Centers for Disease Control and Prevention warns that raw or undercooked wild game, including bear meat, can carry trichinella parasites, which cause trichinellosis.

From Salon ● Aug. 8, 2026

As the handbook Ad Herennium—which, attributed to Cicero, had a central role in medieval and Renaissance rhetoric— warns, “That is faulty which is said against the convictions of the judge or of the audience.”

From "Words Like Loaded Pistols" by Sam Leith

Heathrow Airport has warned access to Terminals 2 and 3 is restricted because of flooding.

From BBC ● Aug. 15, 2026

Berner warned that new homeowners should not get hung up on their home’s value after they move in, as it could lead to unnecessary anxiety.

From MarketWatch ● Aug. 15, 2026

According to interviews and internal emails reviewed by ProPublica, career staffers at the Justice Department warned that transferring voter rolls to HSI to enable it to search for noncitizen voters could violate federal privacy laws.

From Salon ● Aug. 15, 2026

A tsunami warning was later lifted but people were warned not to return to damaged buildings for fear that aftershocks may bring them down.

From Barron's ● Aug. 15, 2026

Before Father Julien left the United States, an Army captain named Robert Jones warned him not to go.

From "At Last She Stood" by Erin Entrada Kelly

Before that, the most recent Hindenburg cluster warning flashed on Sept. 14, 2018.

From MarketWatch ● Aug. 15, 2026

A warning from the prime minister that "Britain is a 'tinderbox'," leads the Financial Times.

From BBC ● Aug. 15, 2026

Research in 2022 estimated that more than 14 percent of the global population has had the disease, warning that transmission rates could increase as climate change brings longer, drier summers.

From Barron's ● Aug. 14, 2026

Lores, the former CEO of HP, assumed PayPal’s top job in March after it issued a profit warning, succeeding former CEO Alex Chriss.

From The Wall Street Journal ● Aug. 14, 2026

“We’re fine,” Celia replies, shooting a warning glance at me, and then— very, very slowly—she backs out of the driveway and into the empty street.

From "Keeping Pace" by Laurie Morrison

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023