Source : Webster's Revised Unabridged Dictionary (1913)

Amethyst \Am"e*thyst\, [F. ametiste, amatiste, F. am['e]thyste,
   L. amethystus, fr. Gr. ? without drunkenness; as a noun, a
   remedy for drunkenness, the amethyst, supposed to have this
   power; 'a priv. + ? to be drunken, ? strong drink, wine. See
   {Mead}.]
   1. (Min.) A variety of crystallized quartz, of a purple or
      bluish violet color, of different shades. It is much used
      as a jeweler's stone.

   {Oriental amethyst}, the violet-blue variety of transparent
      crystallized corundum or sapphire.

   2. (Her.) A purple color in a nobleman's escutcheon, or coat
      of arms.

Source : WordNet®

amethyst
     adj : of a moderate purple color

amethyst
     n : a transparent purple variety of quartz; used as a gemstone