Definition of alert

< Aleppo

Alessandria >

a·lert    (-lûrt) KEY 

ADJECTIVE:

1. Vigilantly attentive; watchful: alert to danger; an alert bank guard. See Synonyms at aware.
2. Mentally responsive and perceptive; quick.
3. Brisk or lively in action: the bird's alert hopping from branch to branch.

NOUN:

1. A signal that warns of attack or danger: Sirens sounded the alert for an air raid.
2. A condition or period of heightened watchfulness or preparation for action: Nuclear-armed bombers were put on alert during the crisis.

TRANSITIVE VERB:
a·lert·ed, a·lert·ing, a·lerts

To notify of approaching danger or action; warn: a flashing red light that alerted motorists to trouble ahead.

IDIOM:
on the alert

Watchful and prepared for danger, emergency, or opportunity: bird watchers on the alert for a rare species.

---

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

OTHER FORMS:
a·lertly(Adverb), a·lertness(Noun)