Wiktionary
summer's day
n. A day in summer.
Wikipedia
Summer's Day
Summer's Day is a painting by French Impressionist painter Berthe Morisot. The painting depicts two women seated in a row boat, and was painted in the Bois de Boulogne. It is currently held by the National Gallery, having been donated by Hugh Lane. The painting was stolen from the Tate by two Irish students while it was on display there in order to protest the Lane Bequest. It was later returned after being left anonymously at the Irish Embassy.
Usage examples of "summer's day".
For a moment, just an instant, one side of his face seemed to waver, like heat off a rock on a summer's day, but then the faint distortion was gone.