\Si*de"re*al\, a. [L. sidereus, from sidus, sideris, a
constellation, a star. Cf. {Sideral}, {Consider}, {Desire}.]
1. Relating to the stars; starry; astral; as, sidereal
   astronomy.
2. (Astron.) Measuring by the apparent motion of the stars;
   designated, marked out, or accompanied, by a return to the
   same position in respect to the stars; as, the sidereal
   revolution of a planet; a sidereal day.
{Sidereal clock}, {day}, {month}, {year}. See under {Clock},
   {Day}, etc.
{Sideral time}, time as reckoned by sideral days, or, taking
   the sidereal day as the unit, the time elapsed since a
   transit of the vernal equinox, reckoned in parts of a
   sidereal day. This is, strictly, apparent sidereal time,
   mean sidereal time being reckoned from the transit, not of
   the true, but of the mean, equinoctial point.