Amethyst reaches Middle English amatiste and Latin amethystus. The Greek gemstone name améthystos is related to an adjective meaning not intoxicated.
The source records both French and Latin input into Middle English. The selected cards compress French, and choose one of two Greek noun forms. The supposed effect on drunkenness is a historical belief.
Sources
- Merriam-Webster: amethyst
Word History distinguishes the Greek noun and adjective, gives the selected spellings and records French as well as Latin input.
- logeion.uchicago.edu · amethystus
Meanings of the older forms on the word path.