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sidereal day

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noun Astronomy.
  1. the interval between two successive passages of the vernal equinox over the meridian, being about four minutes shorter than a mean solar day.

Origin of sidereal day

First recorded in 1785–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for sidereal day

sidereal day

noun
  1. See day (def. 5)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012