From Longman Dictionary of Contemporary Englishsummer solsticeˌsummer ˈsolstice noun [singular] TMCthe longest day in the northern hemisphere (=top half of the Earth), around June 22nd
Examples from the Corpus
summer solstice• For instance, by the summer solstice on 21 June, the crops should be long since planted in the ground.• This was probably based on careful observation of the summer solstice.• Astronomers say that many of the medicine wheels on the Great Plains are aligned to the summer solstice.• The day of my visit was the summer solstice, June 21. 