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.
Origin: 1200–50; < ME < OF < L sōlstitium, equiv. to sōl sun + -stit-, comb. form of stat-, var. s. of sistere to make stand (see stand) + -ium-ium; see -ice)
Either of two times of the year when the sun is at its greatest distance from the celestial equator. The summer solstice in the Northern Hemisphere occurs about June 21, when the sun is in the zenith at the tropic of Cancer; the winter solstice occurs about December 21, when the sun is over the tropic of Capricorn. The summer solstice is the longest day of the year and the winter solstice is the shortest.
A highest point or culmination.
[Middle English, from Old French, from Latin sōlstitium : sōl, sun; see sāwel- in Indo-European roots + -stitium, a stoppage; see stā- in Indo-European roots.] sol·sti'tial (-stĭsh'əl) adj.
Either of the two points on the celestial sphere where the ecliptic (the apparent path of the Sun) reaches its greatest distance north or south of the celestial equator. ◇ The northernmost point of the Sun's path, called the summer solstice, lies on the Tropic of Cancer at 23°27' north latitude. ◇ The southernmost point of the Sun's path, called the winter solstice, lies on the Tropic of Capricorn at 23°27' south latitude.
Either of the two corresponding moments of the year when the Sun is directly above either the Tropic of Cancer or the Tropic of Capricorn. The summer solstice occurs on June 20 or 21 and the winter solstice on December 21 or 22, marking the beginning of summer and winter in the Northern Hemisphere (and the reverse in the Southern Hemisphere). The days on which a solstice falls have the greatest difference of the year between the hours of daylight and darkness, with the most daylight hours at the beginning of summer and the most darkness at the beginning of winter. Compare equinox.
[sol-stis, sohl-] 
stɪs