from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Of, relating to, or concerned with the stars or constellations; stellar.
  • adjective Measured or determined by means of the apparent daily motion of the stars.

from The Century Dictionary.

  • Pertaining or relating to the constellations or fixed stars; consisting of or constituted by fixed stars: as, the sidereal regions; sidereal calculations; a sidereal group or system.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective Relating to the stars; starry; astral.
  • adjective (Astron.) 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
  • adjective See under Clock, Day, etc.
  • adjective time as reckoned by sideral days, or, taking the sidereal day as the unit, the time elapsed since a transit of the vernal equinox, reckoned in parts of a sidereal day. This is, strictly, apparent sidereal time, mean sidereal time being reckoned from the transit, not of the true, but of the mean, equinoctial point.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Of or relating to the stars.
  • adjective astronomy Relating to a measurement of time relative to the position of the stars.
  • adjective astronomy Relating to a measurement of time relative to the point of the vernal equinox.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adjective of or relating to the stars or constellations
  • adjective (of divisions of time) determined by daily motion of the stars


from The American Heritage® Dictionary of the English Language, 4th Edition

[From Latin sīdereus, from sīdus, sīder-, constellation, star.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

Latin sidereus, from sidus, sider-, star


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  • This is the difference between what we call the sidereal day (the time that it takes to make one complete rotation) and the synodic day (the time that it takes to go from the Sun highest in the sky until the Sun is again at its highest in the sky).

    Astroprof's Page 2009

  • Kepler, Galileo, and Newton in the seventeenth century, were the means of effecting a rapid advance in the science of astronomy; but that branch of it known as sidereal astronomy was not then in existence.

    The Astronomy of Milton's 'Paradise Lost' Thomas Nathaniel Orchard

  • It's called sidereal or Vedic astrology, and it's popular in India.

    Astrologers struggle with slippage between constellations, horoscope signs Robert McCartney 2011

  • What they are probably thinking is that the imaginary line mentioned above from the earth to the sun sweeps out a full circle in one year; this is called a sidereal year: the time it takes for the sun to appear in the same place against the backdrop of the fixed stars.

    A Great Leap…Forward? John 2008

  • Indeed, little was known of those orbs until within the past hundred years, when the exploration of the heavens by the aid of greatly increased telescopic power, was the means of creating a new branch of astronomical science, called sidereal astronomy.

    The Astronomy of Milton's 'Paradise Lost' Thomas Nathaniel Orchard

  • The time which the earth occupies in making a complete rotation around this axis is called a sidereal day.

    The Story of the Heavens 1876

  • As in connection with 1: 7 the idea of a kind of sidereal ocean had to be rejected as a purely fanciful notion of commentators, so here.

    Exposition of Genesis: Volume 1 1892-1972 1942

  • While I agree that talking about the misogyny is important, it's kind of sidereal to the point I was trying to make, which was that my childhood and teen years as a trans person shaped my socialization and upbringing in ways that aren't acknowledged.

    Questioning Transphobia 2008

  • The whole sidereal system coruscated, reeled and fell in flame.

    Chapter 11 2010

  • In other words, everybody has two signs - one linked to the seasons (Western tradition) and the other more closely linked to the constellations (sidereal).

    Astrologers struggle with slippage between constellations, horoscope signs Robert McCartney 2011


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  • Truly one of my favourite words - for the spelling/pronunciation divide as much as the meaning.

    January 23, 2007

  • "Sidereal, or siderial, something relating to the stars; as, Sidereal Year; Day, &c. being those marked out by the stars.

    "Sidereal Day, is the time in which any star appears to revolve from the meridian to the meridian again, which is 23 hours 56' 4" 6"' of mean solar time, there being 366 sidereal days in a year...."

    Falconer's New Universal Dictionary of the Marine (1816), 472

    October 13, 2008

  • From the suns and stars that plunge forever through sidereal space to the electrons that whirl like mad dervishes within the atom, every particle of living matter is in movement.

    Frank Crane, George Westinghouse: His Life and Achievements

    July 24, 2011

  • the side of royalty (real)

    September 23, 2011

  • "Sidereal distinctively refers rather to stars in the aggregate or as arranged in constellations or groups than to a star considered singly. It is, therefore, not a precise synonym of stellar or astral, and still less, of course, of starry; although in many phrases it is interchangeable with stellar. Thus, the “sidereal spaces” are the “stellar spaces,” and “sidereal gold” is “starry spangles.”" --CD&C

    March 14, 2012

  • Oh, Century! Most romantic of lexicons.

    March 14, 2012