amethyst (n.) Look up amethyst at Dictionary.com
violet-colored quartz, late 13c., amatist, from Old French ametiste (12c., Modern French améthyste) and directly from Medieval Latin amatistus, from Latin amethystus, from Greek amethystos "amethyst," noun use of an adjective, literally "not intoxicating; not drunken," from a- "not" + methyskein "make drunk," from methys "wine," from PIE root *medhu- "honey; mead" (see mead (n.1)).

The stone had a reputation among the ancients for preventing drunkenness; this was perhaps sympathetic magic suggested by its wine-like color. When drinking, people wore rings made of it to ward off the effects. The spelling was restored in early Modern English.