mid-14c., "trial, test of quality, test of character," from Anglo-French assai, ultimately from Late Latin exagium "a weighing" (see essay (n.)). The meaning "trial of purity of a metal" is from late 14c.
by 1979, initialism (acronym) from role-playing game (see roleplay). As an initialism for rocket-propelled grenade, by 1970.
"nine-point scale for test scores," introduced by the U.S. Air Force in 1942, from sta(ndard) + nine.
edible cruciform plant (Eruca sativa) used originally in the Mediterranean region as a salad, 1967, the American English and Australian form of the name (via Italian immigrants), from a dialectal variant of Italian ruchetta, a diminutive form of ruca-, from Latin eruca, a name of some cabbage-like plant (from PIE *gher(s)-uka-, from root *ghers- "to bristle;" for which see horror).
In England, the usual name is rocket (see rocket (n.1)), which is from Italian ruchetta via French roquette. It also sometimes is called hedge mustard.