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

Some Wall Street players warn that the new framework creates hidden risks for public companies.

From The Wall Street Journal ● Oct. 16, 2026

He used an annual speech at the domestic intelligence service's headquarters in London to also warn of rising threats from Iran and "extreme right-wing terrorism".

From BBC ● Oct. 13, 2026

Still, consumer advocates warn that introducing probabilistic rewards into daily retail purchases normalizes speculative risk in everyday life.

From MarketWatch ● Oct. 13, 2026

He urged AI labs to "listen when your scientists warn of severe dangers, investigate unexpected behaviours, and if you can't adequately control the risks, do not release the system".

From Barron's ● Oct. 12, 2026

Now, as Nine had tried to warn Clare, the animals of Fernlight were unusually protective of their peace.

From "The Undead Fox of Deadwood Forest" by Aubrey Hartman

However, the IFS warns that in such a volatile environment, its forecasts are exceptionally uncertain.

From BBC ● Oct. 11, 2026

Spartan Chemical warns that inappropriate exposure can cause the types of effects detainees experienced.

From Los Angeles Times ● Oct. 8, 2026

The securities industry is generating record tax revenue for New York, increasing the city’s and state’s vulnerability to a downturn, the state comptroller warns.

From Barron's ● Oct. 6, 2026

Laycock also warns that AI often flatters users and agrees with them rather than challenging their ideas, creating risks for young people who may accept answers without thinking critically.

From BBC ● Oct. 5, 2026

Pa warns him: “Don’t spoil things in the meantime by acting too hastily.”

From "Vincent and Theo: The Van Gogh Brothers" by Deborah Heiligman

Cornell President Michael Kotlikoff warned in a recent faculty town hall meeting that pushing social events into private houses beyond the school’s purview—“into the shadows”—could exacerbate problems.

From The Wall Street Journal ● Oct. 18, 2026

“Be cautious of unexpected emails, phone calls, or text messages” related to the incident, including claims that the caller is from ETS or the state or a credit monitoring company, officials also warned.

From Los Angeles Times ● Oct. 17, 2026

Officials also warned of poor air quality for residents nearby.

From Barron's ● Oct. 17, 2026

The self-declared modern-day Miss Marple warned Kenny to be on the lookout for anyone acting differently, reasoning that "if you're suddenly a traitor, you're going to be a bit on high alert".

From BBC ● Oct. 17, 2026

Dad’s warned me not to ask too many questions.

From "Code Name Kingfisher" by Liz Kessler

These links, used by Kiran and his friends, have practical downsides – such as frequent buffering or poor quality, or platforms that disappear without warning.

From BBC ● Oct. 18, 2026

A red flag warning, indicating potentially hazardous fire weather, will remain in place through Saturday evening for many parts of Southern California.

From Los Angeles Times ● Oct. 17, 2026

The weather authority said fire danger would remain through much of the day Saturday, warning residents to be prepared for emergency evacuations.

From Barron's ● Oct. 17, 2026

The bond market provided its own warning on what may be overexuberance for an industry group riding the artificial-intelligence build-out — neoclouds, which are pure-play providers of cloud services.

From MarketWatch ● Oct. 16, 2026

“La, I understand why you’re doing this. But fair warning, you’re making a difficult thing nearly impossible.”

From "Split the Sky" by Marie Arnold

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