Merriam-Webster Collegiate Dictionary - solstice

 noun  Etymology: Middle English, from Latin solstitium, from sol sun + -stit-, -stes standing; akin to Latin stare to stand — more at solar, stand  Date: 13th century  1. either of the two points on the ecliptic at which its distance from the celestial equator is greatest and which is reached by the sun each year about June 22 and December 22  2. the time of the sun's passing a ~ which occurs about June 22 to begin summer in the northern hemisphere and about December 22 to begin winter in the northern hemisphere