Alert Definition

ə-lûrt
alerted, alerting, alerts
adjective
Vigilantly attentive; watchful.
Alert to danger; an alert bank guard.
American Heritage
Watchful and ready, as in facing danger.
Webster's New World
Mentally responsive and perceptive; quick.
American Heritage
Quick in thought or action; active; nimble.
Webster's New World
Brisk or lively in action.
The bird's alert hopping from branch to branch.
American Heritage
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noun
alerts
A signal that warns of attack or danger.
Sirens sounded the alert for an air raid.
American Heritage
A warning signal as of an expected air raid; alarm.
Webster's New World
A condition or period of heightened watchfulness or preparation for action.
Nuclear-armed bombers were put on alert during the crisis.
American Heritage
The period during which such a warning is in effect.
Webster's New World
A notice or reminder about some pressing matter or important information.
An alert to drivers about a detour.
Webster's New World
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verb
alerted, alerting, alerts
To notify of approaching danger or action; warn.
A flashing red light that alerted motorists to trouble ahead.
American Heritage
To warn to be ready or watchful.
The troops were alerted.
Webster's New World
To inform or make aware of.
We alerted them to their duties.
Webster's New World
The definition of alert is to take action and warn people to be aware of something that has happened in the past, is presently occurring, or will happen in the future.
When a person runs from door to door ringing bells and shouting about a fire, it is an example of alerting a neighborhood to danger.
YourDictionary

To give warning to.

Wiktionary
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idiom
on the alert
  • Watchful and prepared for danger, emergency, or opportunity:

    bird watchers on the alert for a rare species.

American Heritage
on the alert
  • watchful; vigilant
Webster's New World

Other Word Forms of Alert

Noun

Singular:
alert
Plural:
alerts

Idioms, Phrasal Verbs Related to Alert

Origin of Alert

  • French alerte from Italian all' erta on the lookout alla to the, on the (from Latin ad illam to that) (ad to ad–) (illam) (feminine accusative sing. of ille that, the al-1 in Indo-European roots) erta lookout (from) (past participle of ergere to raise) (from Latin ērigere erect)

    From American Heritage Dictionary of the English Language, 5th Edition

  • From French alerte (“alert”), from the phrase à l'erte (“on the watch”), from Italian all'erta (“to the height”), from erta (“lookout, tower”).

    From Wiktionary

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