Crys·tal n.
 1. Chem. & Min. The regular form which a substance tends to assume in solidifying, through the inherent power of cohesive attraction. It is bounded by plane surfaces, symmetrically arranged, and each species of crystal has fixed axial ratios. See Crystallization.
 2. The material of quartz, in crystallization transparent or nearly so, and either colorless or slightly tinged with gray, or the like; -- called also rock crystal. Ornamental vessels are made of it. Cf. Smoky quartz, Pebble; also Brazilian pebble, under Brazilian.
 3. A species of glass, more perfect in its composition and manufacture than common glass, and often cut into ornamental forms. See Flint glass.
 4. The glass over the dial of a watch case.
 5. Anything resembling crystal, as clear water, etc.
    The blue crystal of the seas.   --Byron.
 Blood crystal. See under Blood.
 Compound crystal. See under Compound.
 Iceland crystal, a transparent variety of calcite, or crystallized calcium carbonate, brought from Iceland, and used in certain optical instruments, as the polariscope.
 Rock crystal, or Mountain crystal, any transparent crystal of quartz, particularly of limpid or colorless quartz.