noun

1. Geom. a solid figure whose ends are parallel, polygonal, and equal in size and shape, and whose sides are parallelograms
2. a crystalline body whose lateral faces meet at edges that are parallel to each other
3. anything that refracts light, as a drop of water
4. Optics
   1. a transparent body, as of glass, whose ends are equal and parallel triangles, and whose three sides are parallelograms: used for refracting or dispersing light, as into the spectrum
   2. any similar body of three or more sides

Etymology: LL prisma < Gr, lit., something sawed < prizein, to saw < priein, to saw, bite; ? akin to Alb prish, (I) destroy, break