The Oxford Thesaurus An A-Z Dictionary of Synonyms - alert adj.

1) awake, wide awake, watchful, vigilant, attentive, heedful, wary, cautious, on the qui vive, aware, on guard, on the lookout, observant, Colloq on the ball, on one's toes: The sentinels must remain alert throughout the night. Kenneth is alert to the perils of smoking cigarettes. 2) active, nimble, lively, agile, active, quick, spry, sprightly, vivacious: He is an alert and joyous old soul. --n. 3) lookout: She is always on the alert for new ways of saving money. 4) alarm, warning, signal, siren: Sound the air-raid alert! --v. 5) warn, caution, advise, alarm, forewarn, signal, notify: We must alert him to the fact that the man is a vicious killer.