n. In geometry, a solid whose bases or ends are any similar, equal, and parallel plane polygons, and whose sides are parallelograms.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.n. In crystallography, a form consisting of planes, usually four, six, eight, or twelve, which are parallel to the vertical axis.n. In canals, a part of the water-space in a straight section of a canal, considered as a parallelepiped.n. In weaving, same as pattern-boxn. A form of illuminator consisting of a prism with two convex surfaces, by which the light is brought to a focus upon the object.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.