Definify.com
Webster 1913 Edition
Siderostat
Sid′er-o-stat
,Noun.
[L.
sidus
, sideris
, a star + Gr. [GREEK][GREEK][GREEK] standing, fixed, fr. [GREEK][GREEK][GREEK][GREEK] 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
.