a transparent polygonal solid, often having triangular ends and rectangular sides, for dispersing light into a spectrum or for reflecting and deviating light. They are used in spectroscopes, binoculars, periscopes, etc
2.
a form of crystal with faces parallel to the vertical axis
3. mathematics
a polyhedron having parallel, polygonal, and congruent bases and sides that are parallelograms
Word origin
C16: from Medieval Latin prisma, from Greek: something shaped by sawing, from prizein to saw