A species of rock-crystal supposed to prevent intoxication (Greek, a-methusta, the antidote of intoxication). Drinking-cups made of amethyst were supposed to be a charm against inebriety.
It was the most cherished of all precious stones by Roman matrons, from the superstition that it would preserve inviolate the affection of their husbands.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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