prism > define

noun

• A polyhedron with two congruent and parallel faces (the bases) and whose lateral faces are parallelograms.
• Optical device having a triangular shape and made of glass or quartz; used to deviate a beam or invert an image.
  • synonyms: optical prism

• (n.) A form the planes of which are parallel to the vertical axis. See Form, n., 13.
• (n.) A solid whose bases or ends are any similar, equal, and parallel plane figures, and whose sides are parallelograms.
• (n.) A transparent body, with usually three rectangular plane faces or sides, and two equal and parallel triangular ends or bases; -- used in experiments on refraction, dispersion, etc.