e·qui·nox (ekwə-nŏks′, ĕkwə-)
1. Either of two points on the celestial sphere at which the ecliptic intersects the celestial equator.
2. Either of the two times during a year when the sun crosses the celestial equator and when the length of day and night are approximately equal; the vernal equinox or the autumnal equinox.
[Middle English, fromOld Frenchequinoxe, fromMedieval Latinaequinoxium, fromLatinaequinoctium : aequi-, equi- + nox, noct-, night; see nekw-t- in the Appendix of Indo-European roots.]
(click for a larger image)equinox
celestial sphere showing the positions of the autumnal and vernal equinoxes
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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