1560s, a type of solid figure, from Late Latin prisma, from Greek prisma (Euclid), literally "something sawed," from prizein "to saw" (see prion). Meaning in optics is first attested 1610s.
prism (prĭz'əm)
n.
A solid figure whose bases or ends have the same size and shape and are parallel to one another, and each of whose sides is a parallelogram.
A transparent body of this form, often of glass and usually with triangular ends, used for separating white light passed through it into a spectrum or for reflecting beams of light.
Such a body used in testing or correcting imbalance of the extrinsic ocular muscles.
A solid figure in geometry with bases or ends of the same size and shape and sides that have parallel edges. Also, an object that has this shape.
Note: A prism of glass (or a similar transparent material) can be used to bend different wavelengths of light by different amounts through refraction. This bending separates a beam of white light into a spectrum of colored light.