alert Definition in the Cambridge English Dictionary
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Definition of “alert” - English Dictionary

Definition of "alert" - American English Dictionary

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alertadjective

 us   /əˈlɜrt/
quick to ​see, ​understand, and ​act in a ​particularsituation: When you’re ​driving, you must ​stay alert. We had to be alert to any ​dangersigns in the ​economy.

alertnoun [C/U]

 us   /əˈlɜrt/
a ​warning to ​people to get ​ready to ​deal with something ​dangerous: [U] The ​police were on the alert for (= ​watchingcarefully for) any ​sign of ​trouble.
alert
verb [T]  us   /əˈlɜrt/
The ​autocompany mailed ​letters to owners of that ​modelcar, alerting them of ​safetyrisks.
(Definition of alert from the Cambridge Academic Content Dictionary © Cambridge University Press)

Definition of "alert" - British English Dictionary

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alertadjective

uk   /əˈlɜːt/  us   /-ˈlɝːt/
C1 quick to ​see, ​understand, and ​act in a ​particularsituation: I'm not ​feeling very alert today - not enough ​sleep last ​night! A ​couple of alert ​readerspostedcomments on the ​websitepointing out the ​mistake. Parents should be alert tosuddenchanges in children's ​behaviour.
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alertness
noun [U] uk   us   /-nəs/

alertnoun [C or U]

uk   /əˈlɜːt/  us   /-ˈlɝːt/
C1 a ​warning to ​people to be ​prepared to ​deal with something ​dangerous: a bomb alert The ​army was put on (​full) alert as the ​peacetalksbegan to ​fail. The ​public were ​warned to be on the alert for (= ​watchingcarefully for)suspiciouspackages.

alertverb [T]

uk   /əˈlɜːt/  us   /-ˈlɝːt/
C2 to ​warn someone of a ​possiblydangeroussituation: An ​anonymousletter alerted ​police to the ​possibility of a ​terroristattack at the ​airport.
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(Definition of alert from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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