warn

American  

[wawrn] / wɔrn /

verb (used with object)

1. 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

2. to urge or advise to be careful; caution.

   to warn a careless driver.

3. to admonish or exhort, as to action or conduct.

   She warned her employees to be on time.

4. to notify, advise, or inform.

   to warn a person of an intended visit.

5. 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.

6. to give authoritative or formal notice to (someone); order; summon.

   to warn a person to appear in court.

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verb (used without object)

1. to give a warning; caution.

   to warn of further disasters.

warn British  

/ wɔːn /

verb

1. to notify or make (someone) aware of danger, harm, etc

2. (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

3. (takes a clause as object or an infinitive) to inform (someone) in advance

   he warned them that he would arrive late

4. (tr; usually foll by away, off, etc) to give notice to go away, be off, etc

   he warned the trespassers off his ground

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Related Words

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

• prewarn verb (used with object)
• rewarn verb (used with object)
• unwarned adjective
• warner noun
• well-warned adjective

Etymology

Origin of warn

First recorded before 1000; Middle English warnen, Old English warnian; cognate with German warnen; 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."

Example Sentences

They also warn the rules could be misused to target critics and clamp down on dissent.

From BBC • Apr. 9, 2026

Analysts forecast Q4 Brent crude at $80, but warn of $100-$115 if the Strait of Hormuz reopening is delayed or production is not restored.

From Barron's • Apr. 9, 2026

Many times I’m driving through the city, and I think of her words — she was trying to warn us.

From Los Angeles Times • Apr. 9, 2026

Iranian hackers are targeting US energy and water sectors, federal agencies warn.

From MarketWatch • Apr. 8, 2026

“Really,” she said disgustedly, “if the cute janitor wanted to warn you, he should have provided a few more details. Names, dates—something you could go to the police with.”

From "Found" by Margaret Peterson Haddix

Related Words

• address
• advise
• alert
• caution
• hint
• inform
• instruct
• notify
• order
• predict
• prepare
• prompt
• recommend
• remind
• signal
• suggest
• summon
• tell
• threaten
• urge