Webster’s Revised Unabridged Dictionary · 1913
Siderostat
Sid′er·o·stat (sĭd′ẽr·ō·stăt), n. [L. sidus, sideris, a star + Gr. στατός standing, fixed, fr. ἑστάναι 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.