'Indian summer'

The expression 'Indian summer' has been used for more than two centuries. The earliest known use was by French-American writer John Hector St. John de Crevecoeur in rural New York in 1778: "Then a severe frost succeeds which prepares it to receive the voluminous coat of snow which is soon to follow; though it is often preceded by a short interval of smoke and mildness, called the Indian Summer."

Similar usages in Europe:  In former times in Europe, 'Indian summer' was called 'Saint Martin's Summer', referring to St. Martin's day, November 11, when it was supposed to end.