solstice

solstice \SOL-stis, SOHL-\, noun:

1. Astronomy. a. either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, or about December 22, when it reaches its southernmost point. Compare summer solstice, winter solstice. b. either of the two points in the ecliptic farthest from the equator.
2. a furthest or culminating point; a turning point.

...the Sun appears a second time to be in the Plane of the Equinoctial Circle, in its Passage from the Winter Solstice to the SummerSolstice...
-- John Shuttleworth, A Treatise of Astronomy, 1738

The era, a purely astronomical division of time, began with the coincidence of the December solstice with perihelion, and was renewed every 25,765 years.
-- Camille Flammarion, Omega: The Last Days of the World, 1894

Solstice comes from the Latin solstitium referring to when the sun stands still. It entered English in the 1200s.