crys·tal 
(krĭstəl)
(krĭstəl)n.
1.
a. A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts.
b. The unit cell of such a pattern.
2. A mineral, especially a transparent form of quartz, having a crystalline structure, often characterized by external planar faces.
3.
a. A natural or synthetic crystalline material having piezoelectric or semiconducting properties.
b. An electronic device containing such a material, as one that provides access to a radio frequency.
4.
a. A high-quality, clear, colorless glass.
b. An object, especially a vessel or ornament, made of such glass.
c. Such objects considered as a group.
5. A clear glass or plastic protective cover for the face of a watch or clock.
6. Slang A stimulant drug, usually methamphetamine, in its powdered form.
adj.
Clear or transparent: a crystal lake; the crystal clarity of their reasoning. See Synonyms at clear.
[Middle English cristal, from Old French, from Latin crystallum, from Greek krustallos, ice, crystal; see kreus- in the Appendix of Indo-European roots.]
crystalAxes of symmetry in the seven main crystal systems are depicted using different colors. Within each crystal, axes having the same color are of equal length.