alert
Americanadjective
noun
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an attitude of vigilance, readiness, or caution, as before an expected attack.
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a warning or alarm of an impending military attack, a storm, etc..
We'd just boarded the bus when the alert sounded.
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the period during which such a warning or alarm is in effect.
verb (used with object)
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to warn (troops, ships, etc.) to prepare for action.
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to warn of an impending raid, attack, storm, etc..
The radio alerted coastal residents to prepare for the hurricane.
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to advise or warn; cause to be on guard.
to alert gardeners to the dangers of some pesticides.
idioms
adjective
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vigilantly attentive
alert to the problems
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brisk, nimble, or lively
noun
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an alarm or warning, esp a siren warning of an air raid
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the period during which such a warning remains in effect
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on guard against danger, attack, etc
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watchful; ready
on the alert for any errors
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verb
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to warn or signal (troops, police, etc) to prepare for action
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to warn of danger, an attack, etc
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
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Gusty winds are expected in the Coachella Valley region Friday, where an air quality alert is in effect until 3 a.m.
From Los Angeles Times • Apr. 10, 2026
“We need to move faster and stay more alert than ever to prevent any negative impact on the public’s daily life and our economy,” she said.
From The Wall Street Journal • Apr. 10, 2026
The passengers returned to the plane after a brief wait and were preparing to taxi when a second alert hit.
From The Wall Street Journal • Apr. 8, 2026
There was no immediate link made with the war in the Middle East, but Israeli and US diplomatic missions in the region and elsewhere are on heightened alert for any attacks against them.
From Barron's • Apr. 7, 2026
He forced himself to stay alert and to keep shouting.
From "Healer of the Water Monster" by Brian Young
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
