"clear rich-red variety of corundum," c.1300, from Old French rubi (12c.), from Medieval Latin rubinus lapis "red stone" (cf. Italian rubino), from Latin rubeus "red," related to ruber (see red). As a color name from 1570s. As an adjective from late 15c. Modern French rubis is not explained; Klein suggests a plural mistaken for singular.
A deep-red, translucent variety of the mineral corundum, containing small amounts of chromium and valued as a gem. Compare sapphire.