What's the "een" in Halloween?
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.