1. Any of various semiprecious gems such as chrysoberyl, BeAl2O 4, reflecting a band of light that shifts position as the gem is turned.
2. A glass or plastic reflector designed to glow in the beam of a headlight, used on a vehicle as a safety device or set in rows along a highway as lane markers.
3. A marble having an eyelike design, such as concentric circles or a colored center set in clear glass.