- 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.
verb (used with object)
- 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.
adjective (usually postpositive)
- vigilantly attentivealert to the problems
- brisk, nimble, or lively
- 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; readyon the alert for any errors
- 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. Watchful, fully prepared, as in The inspectors are always on the alert for a manufacturing error. [Late 1700s] see on the alert.