adjective Astronomy.
determined by or from the stars: sidereal time.
of or pertaining to the stars.

1625–35; < Latin sīdere(us) of, belonging to the stars (sīder-, stem of sīdus star, constellation + -eus adj. suffix) + -al1

sidereally, adverb
nonsidereal, adjective
unsidereal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
sidereal (saɪˈdɪərɪəl)
1.  of, relating to, or involving the stars
2.  determined with reference to one or more stars: the sidereal day
[C17: from Latin sīdereus, from sīdus a star, a constellation]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1634, "of or pertaining to the stars," earlier sideral (1594), from Fr. sidereal (16c.), from L. sidereus "starry, astral," from sidus (gen. sideris) "star, constellation," probably from PIE base *sweid- "to shine" (cf. Lith. svidus "shining, bright").
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
sidereal   (sī-dîr'ē-əl)  Pronunciation Key 
  1. Relating to the stars or constellations.

  2. Measured with respect to the background of fixed stars instead of the Sun.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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