Lachlan Kincaid age 12 of Dallas, T. C, s .for a question:

Our language was invented by the smart ancestors of the English. But when it comes to Indian summer, the British have learned a word or two from the Americans. Since time began, the seasons have followed one another ‑ spring, summer, fall and winter. This happens both in Europe and America. Both regions also have unseasonable spells. Often there is a warm spell in the late fall or early winter when everyone is expecting frost and cold.

For generations, the English called this spell of pleasant weather by various names. It was known as Allhallow summer, St. Austin’s summer, St. Luke's summer or St. Martins summer. This was because these feast days occurred at this time of year. The American settlers found that the Indians used this short spell of unexpected summer to prepare for winter. They named it Indian summer and the English have borrowed the expression. Though, they have no Indians, they now have Indian summer in Britain.