equinox

Noun

equinox (plural equinoxes or (rare) equinoctes)

1. One of two times in the year (one in March and the other in September) when the length of the day and the night are equal, which occurs when the sun is directly overhead at the equator; this marks the beginning of spring in one hemisphere and autumn in the other.
   • [T]he Months of March and September, the tvvo Æquinoxes of Our year, are the moſt vvindy and tempeſtuous, the moſt unſettled and unequable of Seaſons in moſt Countries of the VVorld.1692 December 15, Richard Bentley, A Confutation of Atheism from the Origin and Frame of the World. The Third and Last Part. […], London: […] H[enry] Mortlock […], published 1693, →OCLC, pages 25–26
   • The four grand and ſolemn Bardic days are, of ancient uſage, the tvvo equinoxes, and the tvvo ſolſtices; the nevv and full moons are alſo, ſubordinately, ſolemn Bardic days: […]1793 September 22, Edward Williams, “Ode on Converting a Sword into a Pruning Hook”, in Poems, Lyric and Pastoral. […], London: […] J[ohn] Nichols; […], published 1794, →OCLC, footnote *, pages...

   Synonyms:

   evennight

2. (also, figuratively) The circumstance of a twenty-four hour time period having the day and night of equal length.
   • [D]oe but ſee his vice, / Tis to his vertue, a iuſt equinox, / The one as long as th'other: […]c. 1603–1604 (date written), William Shakespeare, The Tragœdy of Othello, the Moore of Venice. […] (First Quarto), London: […] N[icholas] O[kes] for Thomas Walkley, […], published 1622, →OCLC, [Act...
3. One of the two points in space where the apparent path of the Sun intersects with the equatorial plane of the Earth.
4. (obsolete, rare) A gale (“very strong wind”) once thought to occur more frequently around the time of an equinox (sense 1), now known to be a misconception; an equinoctial gale.
   • The paſſage yet vvas good, the vvind, 'tis true, / VVas ſomevvhat high, but that vvas nothing nevv, / Nor more than uſual Equinoxes blevv.1687, [John Dryden], “The Third Part”, in The Hind and the Panther. A Poem, in Three Parts, 2nd edition, London: […] Jacob Tonson […], →OCLC, page 101
   • The Equinox drove the sand into their faces or round their legs, as they dived among the sheep-haunted hollows.1920 September 1, Rudyard Kipling, “The Satisfaction of a Gentleman”, in The London Magazine, London: Hunt and Clarke, […], →OCLC; republished on the website of The Kipling Society, accessed 7...
5. (obsolete) A celestial equator (“great circle on the celestial sphere, coincident with the plane of the Earth's equator (the equatorial plane)”); also, the Earth's equator.
   • [T]hey [seals] are over all the American Coaſt of the South Seas, from Terra del Fuego, up to the Equinoctial Line: but to the North of the Equinox again, in theſe Sea, I never ſavv any, till as far as 21 North Lat[itude].1697, William Dampier, chapter IV, in A New Voyage Round the World. […], London: […] James Knapton, […], →OCLC, page 90

   Synonyms:

   equinoctial line