English Reference
adjective · verb · noun

alert

adj. · v. · n.
US /əˈɫɝt/ UK /ɐlˈɜːt/ alert UK spelling alerting, alerts

  1. 01 B1 Intermediate

    adj.watching and listening carefully so that you notice things quickly.

    adj.fully aware and attentive; wide awake and ready to act or respond.

    Simple

    The security guard stayed alert throughout the night to keep the building safe.

    In context

    Despite the long hours of the flight, the pilot remained alert and responded immediately to the slight change in engine vibration.

    inattentiveoblivious
  2. 02 B2 Upper Intermediate

    v.to tell someone about a danger or a problem so they can be ready.

    v.to notify someone of a potential danger, problem, or important event.

    Simple

    A neighbor called to alert us that our garage door was still open.

    In context

    The intelligence agency acted quickly to alert the local authorities about the credible threat to the public event.

  3. 03 B1 Intermediate

    n.a message or signal that warns people of danger.

    n.a signal, such as a siren or digital notification, that warns of an immediate danger or important condition.

    Simple

    The phone sent out a loud alert to warn everyone about the coming storm.

    In context

    The system triggered an automatic alert when the server temperature exceeded the safe operating limit.

  4. 04 B2 Upper Intermediate Military

    n.a state of being ready for a sudden attack or danger.

    n.a condition of heightened watchfulness or preparation for action, especially in a military or emergency context.

    Simple

    The army was on high alert after the peace talks failed.

    In context

    The coastal defenses were placed on full alert following reports of unidentified vessels entering territorial waters.

Usage alert system · alert warning · alerts issued

The 2-mile-long fire front, with flames up to 30 metres (98ft) high, was brought under control later in the day, the regional civil protection chief said, though crews remained on alert for flare-ups.

The Guardian· 14 Aug 2026

The flight crew’s timeline of the event was set out by the NTSB, detailing how they experienced a “high vibration” engine alert during the flight climb.

The Guardian· 14 Aug 2026

Etymology 1

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

Etymology 2

Formed within English by conversion, from alert (adjective). Compare French alerter.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Italian all'erta
Level C1 · Advanced
Frequency Common
Updated