Heliostat
Pronunciation : He"li*o*stat
Part of Speech : n.
Etymology : [Helio- + Gr. h?liostate.]
Definition : Defn: An instrument consisting of a mirror moved by clockwork, by which a sunbeam is made apparently stationary, by being steadily directed to one spot during the whole of its diurnal period; also, a geodetic heliotrope.
Source : Webster's Unabridged Dictionary, 1913