The Collaborative International Dictionary of English v.0.48:

Ruby \Ru"by\, n.; pl. Rubies. [F. rubis (cf. Pr. robi), LL.
   rubinus, robinus, fr. L. rubeus red, reddish, akin to ruber.
   See Rouge, red.]
   1. (Min.) A precious stone of a carmine red color, sometimes
      verging to violet, or intermediate between carmine and
      hyacinth red. It is a red crystallized variety of
      corundum.
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   Note: Besides the true or Oriental ruby above defined, there
         are the balas ruby, or ruby spinel, a red variety of
         spinel, and the rock ruby, a red variety of garnet.
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               Of rubies, sapphires, and pearles white.
                                                  --Chaucer.
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   2. The color of a ruby; carmine red; a red tint.
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            The natural ruby of your cheeks.      --Shak.
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   3. That which has the color of the ruby, as red wine. Hence,
      a red blain or carbuncle.
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   4. (Print.) See Agate, n., 2. [Eng.]
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   5. (Zool.) Any species of South American humming birds of the
      genus Clytolaema. The males have a ruby-colored throat
      or breast.
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   Ruby of arsenic, Ruby of sulphur (Chem.), a glassy
      substance of a red color and a variable composition, but
      always consisting chiefly of the disulphide of arsenic; --
      called also ruby sulphur.

   Ruby of zinc (Min.), zinc sulphide; the mineral zinc blende
      or sphalerite.

   Ruby silver (Min.), red silver. See under Red.
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