[ sahy-deer-ee-uhl ]
/ saɪˈdɪər i əl /

adjective Astronomy.

determined by or from the stars: sidereal time.
of or relating to the stars.

Origin of sidereal

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


si·de·re·al·ly, adverbnon·si·de·re·al, adjectiveun·si·de·re·al, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Example sentences from the Web for sidereal

British Dictionary definitions for sidereal

/ (saɪˈdɪərɪəl) /


of, relating to, or involving the stars
determined with reference to one or more starsthe sidereal day

Derived forms of sidereal

sidereally, adverb

Word Origin for sidereal

C17: from Latin sīdereus, from sīdus a star, a constellation
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

Scientific definitions for sidereal

[ sī-dîrē-əl ]

Relating to the stars or constellations.
Measured with respect to the background of fixed stars instead of the Sun.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.