either of the two occasions each year when the sun is furthest from the celestial equator and highest or lowest in the sky at noon; 22 June or 22 December
either of the two points on the ecliptic1 (apparent path of the sun) at which the distance from the celestial equator is greatest, passed by the sun each year about 22 June and 22 December
either of the two times, the longest and shortest days of the year, when the sun passes one of these points
solstitial /solʹstish(ə)l/ adj
[Middle English via Old French from Latin solstitium, from sol sun + stitus, past part. of sistere to come to a stop, cause to stand]