[ uh-lurt ]
See synonyms for: alertalertedalertsalertly on

  1. fully aware and attentive; wide-awake; keen: She had an alert mind.

  2. swift; agile; nimble.

  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.

  1. 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.

  1. to advise or warn; cause to be on guard: to alert gardeners to the dangers of some pesticides.

Idioms about alert

  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.

Origin of alert

First recorded in 1590–1600; 1940–45 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

synonym study For alert

1. 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 words for alert

Opposites for alert

Other words from alert

  • a·lert·ly, adverb
  • a·lert·ness, noun
  • hy·per·a·lert, adjective
  • un·a·lert·ed, adjective

Words Nearby alert Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use alert in a sentence

British Dictionary definitions for alert


/ (əˈlɜːt) /

adjective(usually postpositive)
  1. vigilantly attentive: alert to the problems

  2. brisk, nimble, or lively

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

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

  1. on the alert

    • on guard against danger, attack, etc

    • watchful; ready: on the alert for any errors

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

  2. to warn of danger, an attack, etc

Origin of alert

C17: from Italian all'erta on the watch, from erta lookout post, from ergere to build up, from Latin ērigere; see erect

Derived forms of alert

  • alertly, adverb
  • alertness, noun

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Idioms and Phrases with alert


see on the alert.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.