equinox

 
Pronunciation: /ˈiːkwɪnɒks, ˈɛkwɪ-/

noun

  • the time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of equal length (about 22 September and 20 March).
  • another term for equinoctial point.

Origin:

late Middle English: from Old French equinoxe or Latin aequinoctium, from aequi- 'equal' + nox, noct- 'night'