prism

American Heritage® Dictionary of the English Language, Fourth Edition

1. 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.
2. n. 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.
3. n. A cut-glass object, such as a pendant of a chandelier.
4. n. A crystal form consisting of three or more similar faces parallel to a single axis.
5. n. A medium that misrepresents whatever is seen through it.

Century Dictionary and Cyclopedia

1. n. In geometry, a solid whose bases or ends are any similar, equal, and parallel plane polygons, and whose sides are parallelograms. Prisms are triangular, square, pentagonal, etc., according as the figures of their ends are triangles, squares, pentagons, etc.
2. n. Specifically An optical instrument consisting of a transparent, medium so arranged that the surfaces which receive and transmit light form an angle with each other: usually of a triangular form with well-polished sides, which meet in three parallel lines, and made of glass, rock-salt, or quartz, or a liquid, as carbon disulphid, contained in a prismatic receptacle formed of plates of glass. A ray of light falling upon one of the sides of a prism is refracted (see refraction) or bent from its original direction at an angle depending upon its own wave-length, the angle of incidence, the angle of the prism, and the material of which the prism is made. This angle of deviation, as it is called, has a definite minimum (minimum deviation) value when the angle of incidence is equal to the angle of emergence. The angle of deviation increases as the wave-length of the light-ray diminishes; consequently, if a pencil of white light falls upon the prism, the different rays are separated or dispersed, and a spectrum is the result. (See spectrum.) Prisms are hence used in spectrum analysis to decompose light, so that the rays of which it is made up may be examined.
3. n. In crystallography, a form consisting of planes, usually four, six, eight, or twelve, which are parallel to the vertical axis. If the planes intersect the lateral axes at the assumed unit distances for the given species, it is called a unit prism; otherwise it may be described, according to the position of the planes, as a macroprism, brachyprism, orthoprism, or clinoprism. In the triclinic system the form includes two planes only, and it is hence called a hemiprism. In the tetragonal system the unit prism is sometimes called a protoprism, or prism of the first order, and the diametral prism, whose planes are parallel to a lateral axis, a deuteroprism, or prism of the second order; these names are also used in an analogous manner in the hexagonal system.
4. n. In canals, a part of the water-space in a straight section of a canal, considered as a parallelepiped.
5. n. In weaving, same as pattern-box
6. n. A form of illuminator consisting of a prism with two convex surfaces, by which the light is brought to a focus upon the object.
7. n. According to some authors any form having two pairs of parallel faces is called a prism; in this sense the term includes the domes of the orthorhombic system (this name being then restricted to a form having two faces only intersecting in an edge) and the hemipyramids of the monoclinic system.

Wiktionary

1. n. geometry A polyhedron with parallel ends of the same size and shape, the other faces being parallelogram-shaped sides.
2. n. A transparent block in the shape of a prism (typically with triangular ends), used to split or reflect light.
3. n. A crystal in which the faces are parallel to the vertical axis.

GNU Webster's 1913

1. n. (Geom.) A solid whose bases or ends are any similar, equal, and parallel plane figures, and whose sides are parallelograms.
2. n. (Opt.) A transparent body, with usually three rectangular plane faces or sides, and two equal and parallel triangular ends or bases; -- used in experiments on refraction, dispersion, etc.
3. n. (Crystallog.) A form the planes of which are parallel to the vertical axis. See Form, n., 13.

WordNet 3.0

1. n. a polyhedron with two congruent and parallel faces (the bases) and whose lateral faces are parallelograms
2. n. optical device having a triangular shape and made of glass or quartz; used to deviate a beam or invert an image