—adj.
1 watchful or vigilant; ready to take action.
2 nimble (esp. of mental faculties); attentive.
—n.
1 a warning call or alarm.
2 a warning of an air raid. b the duration of this.
—v.tr. (often foll. by to) make alert; warn (were alerted to the danger).
Phrases and idioms:
on the alert on the lookout against danger or attack.
Derivatives:
alertly adv. alertness n.
Etymology: F alerte f. It. all' erta to the watch-tower
Useful english dictionary. 2012.