Longman Dictionary of Contemporary English homepage

Language: Old English
Origin: warnian

warn

verb
     
warn S3 W2 [intransitive and transitive]
1 to tell someone that something bad or dangerous may happen, so that they can avoid it or prevent it:
'Be careful, the rocks are slippery,' Alex warned.
warn somebody about something
Travellers to Africa are being warned about the danger of HIV infection.
warn (somebody) of something
Salmon farmers are warning of the severe crisis facing the industry.
warn somebody (not) to do something
I warned you not to walk home alone.
Motorists are being warned to avoid the centre of London this weekend.
warn somebody (that)
We warned them that there was a bull in the field.
2 to tell someone about something before it happens so that they are not worried or surprised by it
warn somebody (that)
Warn her you're going to be back late.

warn (somebody) against something

phrasal verb
to advise someone not to do something because it may have dangerous or unpleasant results:
Her financial adviser warned her against such a risky investment.
warn (somebody) against doing something
The police have warned tourists against leaving the main tourist centres.

warn somebody ↔ away

phrasal verb
to tell someone that they should not go near something, especially because it may be dangerous:
The snake's markings are intended to warn away predators.

warn sb↔ off

phrasal verb
1 to tell people that they should not go near something, especially because it might be dangerous:
Some animals mark their territory to warn off rivals.
2 especially British English to tell someone that they should not do or use something because it might be dangerous
warn somebody off doing something
Doctors should have warned people off using the drug much earlier than they did.

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