adj. of or concerning the constellations or fixed stars. sidereal clock a clock showing sidereal time. sidereal day the time between successive meridional transits of a star or esp. of the first point of Aries, about four minutes shorter than the solar day. sidereal time time measured by the apparent diurnal motion of the stars. sidereal year a year longer than the solar year by 20 minutes 23 seconds because of precession.
[ L sidereus f. sidus sideris star ]