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alert

[uh-lurt]
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adjective
  1. fully aware and attentive; wide-awake; keen: an alert mind.
  2. swift; agile; nimble.
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.

Origin of alert

1590–1600; 1940–45 for def 4; < Italian all'erta, equivalent to all(a) to, on the + erta lookout, watchtower, orig. feminine of erto, past participle of ergere < Latin ērigere to erect
Related formsa·lert·ly, adverba·lert·ness, nounhy·per·a·lert, adjectiveun·a·lert·ed, adjective

Synonyms

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1. awake, wary, observant. 2. brisk, lively, quick, active, sprightly, spirited.

Synonym study

1. Alert, vigilant, watchful imply a wide-awake attitude, as of someone keenly aware of his or her 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: watchful waiting.

Antonyms

1. unaware.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for on the alert

alert

adjective (usually postpositive)
  1. vigilantly attentivealert to the problems
  2. brisk, nimble, or lively
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. on the alert
    1. on guard against danger, attack, etc
    2. watchful; readyon the alert for any errors
verb (tr)
  1. to warn or signal (troops, police, etc) to prepare for action
  2. to warn of danger, an attack, etc
Derived Formsalertly, adverbalertness, noun

Word Origin

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

Word Origin and History for on the alert

alert

adv.

"on the watch," 1590s, from French alerte "vigilant" (17c.), from phrase à l'erte "on the watch," from Italian all'erta "to the height," from erta "lookout, high tower," noun use of fem. of erto, past participle of ergere "raise up," from Latin erigere "raise" (see erect). The adjective is attested from 1610s, the noun from 1803, and the verb from 1868. Related: Alerted; alerting.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with on the alert

on the alert

Watchful, fully prepared, as in The inspectors are always on the alert for a manufacturing error. [Late 1700s]

alert

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