sidereal

Etymology

It is partly borrowed from Middle French sidereal (“relating to the stars”), recorded about 1510,^[2][3][4] and partly borrowed from Latin sīdereus (“of the stars or constellations, starlike”) with the English suffix -al.^[2][5][6][7] The Latin adjective is formed from the stem of sīdus (“star, constellation”) with the suffix -eus.^[2][5][8] Etymonline calls the further origin of the noun uncertain.^[4] Barnhart and Klein compare Lithuanian svidus (“shining, bright”) and Latvian svīst (“to dawn”), and probably Old High German swīdan (“to burn”) and Old Norse svíða (“to burn”),^[3][9] from Proto-Indo-European *sweid- (“to shine”).^[3][4] De Vaan considers that link not very specific, and reports a proposal by Rix that the noun and Ancient Greek ἰθύς (īthús, “straight, just”) go back to Proto-Indo-European *seHdʰ- (“to achieve a goal”), with a Proto-Italic noun meaning "mark, target".^[10]

Earliest recorded meaning

Starlike, bright, splendid: 1534, in Whittington's translation of Cicero, in the revised OED.^[2] Barnhart has "starlike" from 1634,^[3] Etymonline from the 1630s,^[4] and Dictionary.com dates the word to 1625–35.^[8] The older form sideral Etymonline dates to the 1590s.^[4]

Semantic evolution

The word first described something that shone like a star, a use the revised OED calls chiefly literary in later use^[2] and the Shorter Oxford of 2002 still took as rare and limited to the 17th century.^[6] The plain relational sense, "of the stars", is recorded from 1639 in the OED,^[2] from the 1640s in Etymonline,^[4] and only from 1647 in Merriam-Webster Unabridged.^[5] The technical astronomical sense, a period of time measured by the apparent passage of the stars, came early (1612) and survives in the names of the sidereal day, month and year;^[2][6] a sidereal day is about four minutes shorter than a solar day.^[4][6] Motion measured against the fixed stars followed in 1686,^[2] which fits Etymonline's date of the 1680s for this technical use.^[4] A timepiece showing sidereal time is recorded from 1767.^[2]

Timeline

• 1534 – starlike, bright, splendid.^[2]
• 1612 – of a period of time, measured by the apparent passage of the stars.^[2]
• 1639 – of or relating to the stars.^[2] Merriam-Webster Unabridged dates it to 1647.^[5]
• 1646 – concerned with the stars as objects of study.^[2]
• 1686 – of the motion of a celestial object, measured against the fixed stars.^[2]
• 1767 – of a clock, showing sidereal time.^[2]

Meanings

Adjective

1. Of or relating to the stars or constellations.^[11][5][2]
2. Measured with reference to the stars rather than the sun: the sidereal day.^[11][2][6]
3. Of a body's motion: measured against the background of the fixed stars.^[2][6]
4. (literary) Like a star; bright, shining.^[2]

Word family

• sidereally
• nonsidereal
• sidereal day
• sidereal hour
• sidereal hour angle
• sidereal minute
• sidereal month
• sidereal second

Related words

• consider
• desire
• sideral

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e f g h Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
5. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ a b c d e f Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
7. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
8. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
9. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
10. ^ de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
11. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins