valuable precious gem, in modern understanding a clear, rich-red variety of corundum, c. 1300, rubi, rubie (late 12c. as a surname), from Old French rubi (12c.), from Medieval Latin rubinus lapis "red stone" (source also of Italian rubino), from Latin rubeus "red," which is related to ruber (from PIE root *reudh- "red, ruddy").
As a name for a pure or somewhat crimson-red color, from 1570s. As an adjective from late 15c., "made from or with rubies;" c. 1500 as "of a ruby color." Modern French rubis is not explained; Klein suggests a plural mistaken for singular.