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crys·tal (krĭstəl)
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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.]
(click for a larger image)
crystal
Axes 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.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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