Alert
late 16th century (originally in military use): from French alerte, from Italian all' erta ‘to the watchtower’.
wiktionary
From French alerte(“alert”), from the phrase à l'erte(“on the watch”), from Italian all'erta(“to the height”), from erta(“lookout, tower”). [1]
Formed within English by conversion, from alert(adj). Compare French alerter. [2]
etymonline
alert (adv.)
"on the watch," 1610s, from French alerte "vigilant" (17c.), from prepositional phrase à l'erte "on the watch," from Italian all'erta "to the height." Second element from erta "lookout, high tower," noun use of fem. of erto, past participle of ergere "raise up," from Latin erigere "raise" (see erect (adj.)).
The adjective is attested from 1712; the noun is from 1796 as "attitude of vigilance" (as in on the alert); 1803 as "a warning report." The verb is by 1864. Related: Alerted; alerting.
