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.
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   4. The glass over the dial of a watch case.
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   5. Anything resembling crystal, as clear water, etc.
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            The blue crystal of the seas.         --Byron.
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   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]

The Collaborative International Dictionary of English v.0.48:

Crystal \Crys"tal\, a.
   Consisting of, or like, crystal; clear; transparent; lucid;
   pellucid; crystalline.
   [1913 Webster]

         Through crystal walls each little mote will peep.
                                                  --Shak.
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         By crystal streams that murmur through the meads.
                                                  --Dryden.
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         The crystal pellets at the touch congeal,
         And from the ground rebounds the ratting hail. --H.
                                                  Brooks.
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WordNet (r) 3.0 (2006):

crystal
    n 1: a solid formed by the solidification of a chemical and
         having a highly regular atomic structure
    2: a crystalline element used as a component in various
       electronic devices
    3: a rock formed by the solidification of a substance; has
       regularly repeating internal structure; external plane faces
       [syn: crystal, crystallization]
    4: colorless glass made of almost pure silica [syn: quartz
       glass, quartz, vitreous silica, lechatelierite,
       crystal]
    5: glassware made of quartz
    6: a protective cover that protects the face of a watch [syn:
       crystal, watch crystal, watch glass]

The Free On-line Dictionary of Computing (19 January 2023):

Crystal

   Concurrent Representation of Your Space-Time ALgorithms.

   A recursion equation parallel language.

   ["A Parallel Language and its Compilation to Multiprocessor
   Machines or VLSI", M.C. Chen, 13th POPL, ACM 1986 pp.131-139].

   (1994-12-06)