/priz"euhm/ , n.
1. Optics. a transparent solid body, often having triangular bases, used for dispersing light into a spectrum or for reflecting rays of light.
2. Geom. a solid having bases or ends that are parallel, congruent polygons and sides that are parallelograms.
3. Crystall. a form having faces parallel to the vertical axis and intersecting the horizontal axes.
[ 1560-70; prisma prîsma lit., something sawed, akin to prízein to saw, pristes sawyer ]