Gem n.
  1. Bot. A bud.
  From the joints of thy prolific stem
  A swelling knot is raised called a gem.   --Denham.
  2. A precious stone of any kind, as the ruby, emerald, topaz, sapphire, beryl, spinel, etc., especially when cut and polished for ornament; a jewel.
  3. Anything of small size, or expressed within brief limits, which is regarded as a gem on account of its beauty or value, as a small picture, a verse of poetry, a witty or wise saying.
  Artificial gem, an imitation of a gem, made of glass colored with metallic oxide.  Cf. Paste, and Strass.