O·pei·do·scope n.  Physics An instrument, consisting of a tube having one end open and the other end covered with a thin flexible membrance to the center of which is attached a small mirror.  It is used for exhibiting upon a screen, by means of rays reflected from the mirror, the vibratory motions caused by sounds produced at the open end of the tube, as by speaking or singing into it.

 ◄ ►