equinox

Etymology

It is borrowed from Old French equinoxe,^[2][3][4] with the Old French variant equinoce of the 12th century,^[5] and directly borrowed from Medieval Latin equinoxium (“equality of night and day”),^[4][5][6][7] the medieval spelling of Latin aequinoctium (“the time of equal days and nights”).^[3][8][6] The Latin noun is formed from aequus (“equal”) and nox (“night”),^[5][8][3] the source of equal and a relative of night.^[8] The OED notes that a late Latin adjective aequinox, also used as a noun for the equinoctial point or sign, seems to occur in Chaucer's use, though it is not the source of the modern word.^[3] Old English had its own translation of the Latin, efnniht.^[5] Barnhart points out that other languages name the event differently, as German Tagundnachtgleiche, literally "day and night equality".^[9]

Earliest recorded meaning

One of the two points where the sun's path crosses the equator: 1391, in Chaucer's Treatise on the Astrolabe (the OED's manuscript is from about 1400).^[3][9][5] The Latin form equinoxium for the same event is used in English before 1398, in Trevisa's Bartholomaeus: Equinoxium is most evenesse of day and nyȝt.^[10]

Semantic evolution

In the OED's record the astronomical point comes first, and the time of year, one of the two periods when day and night are equal all over the earth, follows only in 1588,^[3] although the Middle English use of equinoxium already meant the event.^[10] Shakespeare's Othello is the OED's first record for the condition of equal days and nights, a sense also used figuratively.^[3] Two looser uses died out: the equator itself, from 1579 to 1728, and, once in Dryden (1687), an equinoctial gale.^[3] Johnson (1755) defined equinoxes as the exact times when the sun enters the first points of Aries and Libra, about 21 March and 23 September.^[11]

Timeline

• 1391 – one of the two points where the sun's path crosses the equator, in Chaucer.^[3][9]
• 1579 – the equator (obsolete by 1728).^[3]
• 1588 – one of the two times of the year when day and night are of equal length.^[3]
• before 1616 – the condition of equal days and nights, in Shakespeare's Othello.^[3]
• 1687 – an equinoctial gale, in Dryden (obsolete and rare).^[3]

Meanings

Noun

1. Either of the two times each year, around 20–21 March and 22–23 September, when the sun crosses the celestial equator and day and night are about equal in length: The storm arrived a week after the autumn equinox.^{[6][12][13][2]}
2. Either of the two points on the celestial sphere where the celestial equator meets the ecliptic.^[6][2][12]

Word family

• precession of the equinoxes

Related words

• equinoctial
• equal
• equi-
• night
• nocturnal

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
3. ^ a b c d e f g h i j k l m Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
4. ^ a b Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins
5. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
6. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b c Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ a b c Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
10. ^ a b Kurath, Hans; Kuhn, Sherman M.; Lewis, Robert E., eds. (1952–2001), Middle English Dictionary, Ann Arbor: University of Michigan Press; online edition ed. Frances McSparran et al. (2000–2018)
11. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
12. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins
13. ^ Soanes, Catherine; Stevenson, Angus, eds. (2004), Concise Oxford English Dictionary, 11th ed., Oxford: Oxford University Press