[sidereal day] n (1794): the interval between two successive transits of a point on the celestial sphere (as the vernal equinox) over the upper meridian of a place: 23 hours, 56 minutes, 4.1 seconds of mean time
SIDEREAL DAY
Meaning of SIDEREAL DAY in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012