Crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions.
The word "crystal" comes from the Ancient Greek word κρύσταλλος (krustallos), meaning both "ice" and "rock crystal".
The term "crystal" also refers to:
1. A high-quality glass, especially that used for tableware
2. The transparent cover over the face of a watch
3. A person's clarity of thought or emotional state ("She had a moment of crystal clarity")
4. A slang term for methamphetamine in some contexts