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. prismal adj.
[ LL prisma f. Gk prisma prismatos thing sawn f. prizo to saw ]