Crystal  —n. 1 a transparent colourless mineral, esp. Rock crystal. B piece of this. 2 a highly transparent glass; flint glass. B articles of this. 3 crystalline piece of semiconductor. 4 aggregation of molecules with a definite internal structure and the external form of a solid enclosed by symmetrically arranged plane faces. —adj. (usu. Attrib.) Made of, like, or clear as crystal. [greek krustallos]