1. either of the two times of the year when the sun is at its greatest distance from the celestial equator
The Collaborative International Dictionary of English v.0.48:
Solstice \Sol"stice\, n.[L. solstitium; sol the sun + sistere to
cause to stand, akin to stare to stand: cf. F. solstice. See
Solar, a., Stand, v. i.]
1. A stopping or standing still of the sun. [Obs.] --Sir T.
(a) The point in the ecliptic at which the sun is farthest
from the equator, north or south, namely, the first
point of the sign Cancer and the first point of the
sign Capricorn, the former being the summer solstice,
latter the winter solstice, in northern latitudes; --
so called because the sun then apparently stands still
in its northward or southward motion.
(b) The time of the sun's passing the solstices, or
solstitial points, namely, about June 21 and December
21. See Illust. in Appendix.
WordNet (r) 3.0 (2006):
n 1: either of the two times of the year when the sun is at its
greatest distance from the celestial equator