- pertaining to an equinox or the equinoxes, or to the equality of day and night.
- pertaining to the celestial equator.
- occurring at or about the time of an equinox.
- Botany . (of a flower) opening regularly at a certain hour.
"People who have not navigated the great rivers of equinoctial America can scarcely conceive how, at every instant, without intermission, you may be tormented by insects flying in the air."
- Alexander von Humboldt, as quoted by Elizabeth Kolbert, "Humboldt's gift: He was once the most celebrated naturalist in the world. What happened to him?", 26 October 2015 The New Yorker (http://www.newyorker.com/magazine/2015/10/26/humboldts-gift)