Is it ensure, insure, or assure?
violet quartz, late 13c., ametist, from Old French ametiste (Modern French améthyste) and directly from Medieval Latin amatistus, from Latin amethystus, from Greek amethystos "amethyst," literally "not intoxicating," from a- "not" + methyskein "make drunk," from methys "wine" (see mead (n.1)); based on the stone's ancient reputation for preventing drunkenness, which was perhaps sympathetic magic suggested by its wine-like color. People wore rings made of it before drinking. Spelling restored from Middle English ametist.
one of the precious stones in the breastplate of the high priest (Ex. 28:19; 39:12), and in the foundation of the New Jerusalem (Rev. 21:20). The ancients thought that this stone had the power of dispelling drunkenness in all who wore or touched it, and hence its Greek name formed from _a_, "privative," and _methuo_, "to get drunk." Its Jewish name, _ahlamah'_, was derived by the rabbins from the Hebrew word _halam_, "to dream," from its supposed power of causing the wearer to dream. It is a pale-blue crystallized quartz, varying to a dark purple blue. It is found in Persia and India, also in different parts of Europe.