A-lĕrt’, a.

(14), a. [Fr. alerte, Sp. alerto, from It. all’erta, upon one's guard, on the watch, prop. (standing) upon a declivity, where one is looking around; erti, declivity, steep, slope, erto, steep, p. p. of ergere, erigere, to erect, raise, Lat. erigere; ex, e, from, out of, and regere, to lead straight.]

1. Watchful; vigilant; active in vigilance. Hence the military phrase, upon the alert, upon the watch, guarding against surprise or danger.
2. Brisk; nimble; moving with celerity. “An alert young fellow.” Addison.

Syn.—Brisk; nimble; active; agile; lively; quick; prompt; sprightly; assiduous.