a five-sided prism that deviates light from any direction through an angle of 90°, typically used in single-lens reflex cameras between lens and viewfinder to present the image the right way round
pentaprism in American English
(ˈpentəˌprɪzəm)
noun
a prism that has five faces, a pair of which are at 90° to each other; a ray entering one of the pair emerges from the other at an angle of 90° to its original direction: used esp. in single-lens reflex cameras to reverse images laterally and reflect them to the viewfinder
Also: penta prism
Word origin
[1935–40; penta- + prism]This word is first recorded in the period 1935–40. Other words that entered Englishat around the same time include: aeroembolism, bingo, complementation, fluorocarbon, roomettepenta- is a combining form occurring in loanwords from Greek, meaning “five” (Pentateuch). On this model, penta- is used in the formation of compound words (pentavalent). Other words that use the affix penta- include: Pentateuch, cyclopentadiene, pentaptych, pentatonic scale, pentazocine