A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts. The unit cell of such a pattern. A mineral, especially a transparent form of quartz, having a crystalline structure, often characterized by external planar faces. A natural or synthetic crystalline material having piezoelectric or semiconducting properties. An electronic device, such as an oscillator or detector, using such a material. A high-quality, clear, colorless glass. An object, especially a vessel or ornament, made of such glass. Such objects considered as a group. A clear glass or plastic protective cover for the face of a watch or clock. Slang A stimulant drug, usually methamphetamine, in its powdered form. Clear or transparent: a crystal lake; the crystal clarity of their reasoning.