n.1 a solid geometric figure whose two ends are similar, equal, and parallel rectilinear figures, and whose sides are parallelograms.
2 a transparent body in this form, usu. triangular with refracting surfaces at an acute angle with each other, which separates white light into a spectrum of colours.
Derivatives:
prismal adj.
Etymology: LL prisma f. Gk prisma prismatos thing sawn f. prizo to saw