/ ˈsɒlstɪs; NAmE ˈsɑːl-/ noun
either of the two times of the year at which the sun reaches its highest or lowest point in the sky at midday, marked by the longest and shortest days :
the summer / winter solstice
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WORD ORIGIN
Middle English : from Old French , from Latin solstitium , from sol sun + stit- stopped, stationary (from the verb sistere ).