Baretti: A dictionary of the English and Italian languages
Ért-a, s. f. Ért-o, m. the steep ascent or rising of a hill. V. ertezza. Stare all'—, to stand upon one's guard, to take care. Non saper o poter tenere un cocomero all'—, not to know how to keep a secret.
Florio: a worlde of wordes, or most copious, dictionarie in Italian and English
erta: the vpright beame of any frame, tent, crane, staires or other engine. Also steepie, vpright, high, craggie. Also a steepie, a craggie place, an vpright ascent, a high watch-towre. Also subtile, wilie, watchfull, craftie, quick-sighted, looke Stáre al' erta.