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.

---

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

---

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; 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."

Example Sentences

But Roy Scott was not suspected of any crime—he was the one who called the cops for help, and at no point did the cops warn him that they were going to use force.

From Slate • Apr. 21, 2026

It’s also wise to take coworkers’ investing stories with a grain of salt, said Mark La Spisa, a CFP based in Barrington, Ill. “I always warn people about relying on others’ reported returns,” he says.

From MarketWatch • Apr. 20, 2026

Researchers warn that highly realistic AI-controlled personas could soon play a major role in shaping public opinion and influencing democratic systems.

From Science Daily • Apr. 20, 2026

In the small towns of Kerr County, Mystic is but one piece of a disaster that claimed 119 friends and neighbors from the banks of a river that had no sirens to warn them.

From The Wall Street Journal • Apr. 18, 2026

Now we were close enough to see the skull-and-crossbones posted at intervals on the walls to warn of electrified wiring along the top.

From "The Hiding Place" by Corrie ten Boom

Related Words

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