Siderostat \Sid"er*o*stat\, n. [L. sidus, sideris, a star + Gr.
??? standing, fixed, fr. ???? to place.] (Astron.)
An apparatus consisting essentially of a mirror moved by
clockwork so as to throw the rays of the sun or a star in a
fixed direction; -- a more general term for {heliostat}.
[1913 Webster]