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.
A sidereal period is one with respect to stars. For example, a sidereal day is the time it takes for the stars in the celestial sphere to revolve once. A sidereal year is the time it takes for the Sun to return to the same point in the sky with respect to the stars. See also synodic period.