/pen"teuh priz'euhm/ , n.
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 .
[ 1935-40; PENTA- + PRISM ]