Real Dictionary

solstice
countable noun: The summer solstice is the day of the year with the most hours of daylight, and the winter solstice is the day of the year with the fewest hours of daylight.

solstice in American English
the moment or date when the sun in its apparent annual movement along the ecliptic reaches its maximum distance north or south of the celestial equator: in the Northern Hemisphere, the day of the summer solstice (about June 21, marking the beginning of su
noun: 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

solstice in British English
noun: either the shortest day of the year ( winter solstice) or the longest day of the year ( summer solstice)