mid-15c., rustik, "associated with the country, rural," from Latin rusticus "of the country, rural; country-like, plain, simple, rough, coarse, awkward," from rus (genitive ruris) "open land, country" (see rural).
From 1580s, of persons, "having the look and manner of country folk, wanting refinement." By 1590s of rude or undressed workmanship. By c. 1600 as "plain and simple, having the charm of the country."
The noun meaning "a country person, peasant" is from 1550s (also in classical Latin). Related: Rustical "living in the country," early 15c., rusticalle, from Medieval Latin rusticalis.