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sidereal month

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noun Astronomy.
  1. See under month(def 5).
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Origin of sidereal month

First recorded in 1865–70

month

[muhnth]
noun
  1. Also called calendar month. any of the twelve parts, as January or February, into which the calendar year is divided.
  2. the time from any day of one calendar month to the corresponding day of the next.
  3. a period of four weeks or 30 days.
  4. Also called solar month. one-twelfth of a solar or tropical year.
  5. Also called lunar month. the period of a complete revolution of the moon around the earth, as the period between successive new moons (synodic month), equal to 29.531 days, or the period between successive conjunctions with a star (sidereal month), equal to 27.322 days, or the period between successive perigees (anomalistic month), equal to 27.555 days, or the period between successive similar nodes (nodical month or draconic month), equal to 27.212 days.
  6. an unusually long period of time of indefinite length: I haven't seen him for months.
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Idioms
  1. a month of Sundays. Sunday1(def 4).
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Origin of month

before 900; Middle English; Old English mōnath; cognate with Old High German mānōd, Old Norse mānathr. See moon
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for sidereal month

sidereal month

noun
  1. See month (def. 5)
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month

noun
  1. one of the twelve divisions (calendar months) of the calendar year
  2. a period of time extending from one date to a corresponding date in the next calendar month
  3. a period of four weeks or of 30 days
  4. the period of time (tropical month) taken by the moon to return to the same longitude after one complete revolution around the earth; 27.321 58 days (approximately 27 days, 7 hours, 43 minutes, 4.5 seconds)
  5. the period of time (sidereal month) taken by the moon to make one complete revolution around the earth, measured between two successive conjunctions with a distant star; 27.321 66 days (approximately 27 days, 7 hours, 43 minutes, 11 seconds)
  6. Also called: lunation the period of time (lunar or synodic month) taken by the moon to make one complete revolution around the earth, measured between two successive new moons; 29.530 59 days (approximately 29 days, 12 hours, 44 minutes, 3 seconds)
  7. a month of Sundays informal a long unspecified period
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Related formsRelated adjective: mensal

Word Origin

Old English mōnath; related to Old High German mānōd, Old Norse mānathr; compare Gothic mena moon
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

Word Origin and History for sidereal month

month

n.

Old English monað, from Proto-Germanic *menoth- (cf. Old Saxon manoth, Old Frisian monath, Middle Dutch manet, Dutch maand, Old High German manod, German Monat, Old Norse manaðr, Gothic menoþs "month"), related to *menon- "moon" (see moon (n.); the month was calculated from lunar phases). Its cognates mean only "month" in the Romance languages, but in Germanic generally continue to do double duty. Phrase a month of Sundays "a very long time" is from 1832 (roughly 7 and a half months, but never used literally).

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Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with sidereal month

month

In addition to the idiom beginning with month

also see:

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.