a prism having a highly obtuse angle to facilitate beam splitting
biprism in American English
(ˈbaiˌprɪzəm)
noun
Optics
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: Fresnel biprism
Word origin
[1880–85; bi-1 + prism]This word is first recorded in the period 1880–85. Other words that entered Englishat around the same time include: Chief of Staff, automatism, barnstorm, irredentist, jackpotbi- is a combining form meaning “twice,” “two,” used in the formation of compound words.Other words that use the affix bi- include: biceps, bilabial, bilingual, bipolar, bisect