The Collaborative International Dictionary of English v.0.48:

Crystal \Crys"tal\ (kr[i^]s"tal), n. [OE. cristal, F. cristal,
   L. crystallum crystal, ice, fr. Gr. kry`stallos, fr. kry`os
   icy cold, frost; cf. AS. crystalla, fr. L. crystallum; prob.
   akin to E. crust. See Crust, Raw.]
   1. (Chem. & Min.) The regular form which a substance tends to
      assume in solidifying, through the inherent power of
      cohesive attraction. It is bounded by plane surfaces,
      symmetrically arranged, and each species of crystal has
      fixed axial ratios. See Crystallization.
      [1913 Webster]

   2. The material of quartz, in crystallization transparent or
      nearly so, and either colorless or slightly tinged with
      gray, or the like; -- called also rock crystal.
      Ornamental vessels are made of it. Cf. Smoky quartz,
      Pebble; also Brazilian pebble, under Brazilian.
      [1913 Webster]

   3. A species of glass, more perfect in its composition and
      manufacture than common glass, and often cut into
      ornamental forms. See Flint glass.
      [1913 Webster]

   4. The glass over the dial of a watch case.
      [1913 Webster]

   5. Anything resembling crystal, as clear water, etc.
      [1913 Webster]

            The blue crystal of the seas.         --Byron.
      [1913 Webster]

   Blood crystal. See under Blood.

   Compound crystal. See under Compound.

   Iceland crystal, a transparent variety of calcite, or
      crystallized calcium carbonate, brought from Iceland, and
      used in certain optical instruments, as the polariscope.


   Rock crystal, or Mountain crystal, any transparent
      crystal of quartz, particularly of limpid or colorless
      quartz.
      [1913 Webster]