In antiquity, the word amethyst was indiscriminately applied to almost any purple gemstone, including purple garnet and purple sapphire. The word means "not drunken" because purple stones were credited with the ability to keep drinkers sober no matter how much wine they consumed.  

A late myth described Amethyst as a nymph who loved the wine god.  When he scorned her, Amethyst withered and hardened into a stone that would always oppose the effects of wine.