late 14c., from Old French garniss-, present participle stem of garnir "provide, furnish; fortify, reinforce," from a Germanic stem related to Proto-Germanic *warnejan "be cautious, guard, provide for" (cf. Old High German warnon "to take heed," Old English warnian "to take warning, beware;" see warn). Sense evolution is from "arm oneself" to "fit out" to "embellish," which was the earliest meaning in English, though the others also were used in Middle English. Culinary sense of "to decorate a dish for the table" predominated after c.1700. Older meaning survives in legal sense of "warning of attachment of funds" (1570s). Related: Garnished; garnishing.
late 14c., "set of tableware" (probably a dozen; usually pewter), from garnish (v.). Sense of "embellishments to food" is from 1670s.
overlay with stones (2 Chr. 3:6), adorn (Rev. 21:19), deck with garlands (Matt. 23:29), furnish (12:44). In Job 26:13 (Heb. shiphrah, meaning "brightness"), "By his spirit the heavens are brightness" i.e., are bright, splendid, beautiful.