1) Optical device 
• (n.) A prism whose refracting angle is very nearly 180 degrees. • (n.) A combination of two short rectangular glass prisms cemented together at their diagonal faces so as to form a cube; -- called also optical cube. It is used in one form of photometer.
Bi'prism noun [ Prefix bi- + prism .] 1. A prism whose refracting angle is very nearly 180 degrees. 2. A combination of two short rectangular glass prisms cemented together at their diagonal faces so as to form a cube; -- called also optical cube . It is used in on...
[n] - an optical device for obtaining interference fringes
noun an optical device for obtaining interference fringes
a triangular prism with an apex angle slightly less than 180°: when illuminated by a point source of light it produces two overlapping beams that form an interference pattern on a screen. Also called