·adj Of or pertaining to a solstice.
II. Solstitial ·adj Happening at a solstice; ·esp. (with reference to the northern hemisphere), happening at the summer solstice, or midsummer.
A great circle passing through the poles and solstitial points. ...
The Sailor's Word-Book
The two points where the tropics meet the ecliptic, in longitude 90° and 270°. ...