alert

American  

[uh-lurt] / əˈlɜrt /

adjective

1. fully aware and attentive; wide-awake; keen.

   She had an alert mind.

   Synonyms:

   observant, wary, awake

   Antonyms:

   unaware

2. swift; agile; nimble.

   Synonyms:

   spirited, sprightly, active, quick, lively, brisk

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noun

1. an attitude of vigilance, readiness, or caution, as before an expected attack.

2. a warning or alarm of an impending military attack, a storm, etc..

   We'd just boarded the bus when the alert sounded.

3. the period during which such a warning or alarm is in effect.

verb (used with object)

1. to warn (troops, ships, etc.) to prepare for action.

2. to warn of an impending raid, attack, storm, etc..

   The radio alerted coastal residents to prepare for the hurricane.

3. to advise or warn; cause to be on guard.

   to alert gardeners to the dangers of some pesticides.

idioms

1. on the alert, on guard against danger; in readiness; vigilant.

   The state police are on the alert for an escaped convict believed to be in the area.

alert British  

/ əˈlɜːt /

adjective

1. vigilantly attentive

   alert to the problems

2. brisk, nimble, or lively

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noun

1. an alarm or warning, esp a siren warning of an air raid

2. the period during which such a warning remains in effect

3. 1. on guard against danger, attack, etc

   2. watchful; ready

      on the alert for any errors

verb

1. to warn or signal (troops, police, etc) to prepare for action

2. to warn of danger, an attack, etc

alert More Idioms  

1. see on the alert.

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Usage

What does alert mean? An alert is a warning or alarm, especially an alarm about dangerous weather or a military attack, as in The National Weather Service has alerts for tornadoes, hurricanes, Nor’easters, and other severe weather occurrences. Alert is also an attitude of readiness or caution, as in Tina was on alert for news of her son’s acceptance into college. Alert describes being fully attentive or wide awake, as in Sabine needs to be awake for several hours before she is alert and ready to work. You can be alert to the people and objects surrounding you. When you are alert, you’re ready to act or react instead of being surprised. But you can also be alert to concepts, ideas, and trends, ready to react to a change in others’ thoughts or to a change in the market. To alert means to advise or to warn, as with an alert. For example, your teacher might alert you that your big project is due soon, while a police department might alert the public about a dangerous person on the streets. Example: Alert the security team of the incident and then head home.

Related Words

Alert, vigilant, watchful imply a wide-awake attitude, as of someone keenly aware of their surroundings. Alert describes a ready and prompt attentiveness together with a quick intelligence: The tourist was alert and eager to see the sights. Vigilant suggests some immediate necessity for keen, active observation, and for continuing alertness: Knowing the danger, the scout was unceasingly vigilant. Watchful suggests carefulness and preparedness: A stakeout requires watchful waiting.

Other Word Forms

• alertly
  adverb
• alertness
  noun
• hyperalert
  adjective
• unalerted
  adjective

Etymology

Origin of alert

First recorded in 1590–1600; 1940–45 alert for def. 4; from Italian all'erta, equivalent to all ( a ) “to, on the” + erta “lookout, watchtower,” originally feminine of erto, past participle of ergere from Latin ērigere to erect

Explanation

Alert! Alert! Alert! Did I get your attention? When you are alert, you are awake and ready. When you issue an alert you give warning, alerting people to, or notifying them of, a concern. Alert is one of the rare words that can be used in the same form as a noun, verb, and adjective. In all parts of speech, alert implies preparedness. The word is derived from the French a l'erte which translates to "on the watch." When you hear the word, imagine an alarm going off. The alarm is the alert. When you hear it, you have been alerted and you are now alert.

Example Sentences

Also be on the alert for any signs your financial adviser is sure we’re in—or not in—a bubble.

From The Wall Street Journal • May 8, 2026

But the WHO's emergency alert and response director Abdi Rahman Mahamud insisted: "We believe this will be a limited outbreak if the public health measures are implemented and solidarity shown across all countries."

From Barron's • May 7, 2026

The lawsuit said the shelter failed to alert Moncur that the dog had a known history of aggression due to the cruelty of previous owners.

From Los Angeles Times • May 7, 2026

Asking me not to disclose her full name, Lisa explained how residents remained on alert and used whistles to warn others if immigration agents were seen nearby.

From BBC • May 7, 2026

Whether or not a human knew what they were, an instinct inside them knew to be on alert, to be just a little afraid.

From "Night Owls" by A.R. Vishny

Related Words

• active
• bright
• careful
• intelligent
• observant
• perceptive
• sharp
• vigilant
• wary
• watchful
• wired
• wise