Search

fully aware and attentive; wide-awake; keen:
an alert mind.
swift; agile; nimble.
an attitude of vigilance, readiness, or caution, as before an expected attack.
a warning or alarm of an impending military attack, a storm, etc.:
We’d just boarded the bus when the alert sounded.
the period during which such a warning or alarm is in effect.
to warn (troops, ships, etc.) to prepare for action.
to warn of an impending raid, attack, storm, etc.:
The radio alerted coastal residents to prepare for the hurricane.
to advise or warn; cause to be on guard:
to alert gardeners to the dangers of some pesticides.
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.
Contemporary Examples

Janet Napolitano on the Times Square Bomb: “We Are alerting Everybody to Be on Their Toes”
May 2: 7 Best Moments From Sunday Talk The Daily Beast Video May 1, 2010

On July 8, a summons was sent to Zhang alerting her to the lawsuit, and on July 11, Nan Shi lost her job.
Female Yahoo Exec Accused of Sex Abuse Fires Back Nina Strochlic July 17, 2014

But “with Buster alerting at the rear alley upslope, then that is certainly a possible grave site.”
Can This Dog Solve the Black Dahlia Homicide? Christine Pelisek February 2, 2013

Few would dare to publicly rage against the government, as Gulnara has, for fear of alerting the security services.
Gulnara Karimova’s Tweets Hint at Uzbek Power Struggle Anonymous November 21, 2013

An article had appeared in the local paper a few days before, alerting the community to this gala event.
Remembering William F. Buckley, a Year Later Christopher Buckley February 21, 2009

Historical Examples

But why were they searching for him, alerting the natives in an effort to scoop him up?
The Time Traders Andre Norton

Instead of crippling the nation, they succeeded only in alerting it.
The Last Gentleman Rory Magill

If he did strike, the warning teams would perform their brief mission, alerting the active, working members of the defense groups.
Final Weapon Everett B. Cole

Here the song acquires the additional functions of alerting the female to danger and threatening the trespasser.
Natural History of the Bell Vireo, Vireo bellii Audubon Jon C. Barlow

Instead it washed through his body, sharpening his reflexes and alerting his muscles for action.
Delayed Action Charles Vincent De Vet

adjective (usually postpositive)
vigilantly attentive: alert to the problems
brisk, nimble, or lively
noun
an alarm or warning, esp a siren warning of an air raid
the period during which such a warning remains in effect
on the alert

on guard against danger, attack, etc
watchful; ready: on the alert for any errors

verb (transitive)
to warn or signal (troops, police, etc) to prepare for action
to warn of danger, an attack, etc
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.
Allergy to Latex Education and Resource Team
see: on the alert