A spell of unusually warm and hazy weather in late autumn and the expression dates from the late 18th century. If you were thinking Indian sub-continent and the British Raj, you would be mistaken. The expression is originally American and the Indian reference is to Native American Indians. No one knows for sure why such warm weather was called an Indian summer. One theory (unproven) maintains that it originally had negative connotations because Indian raids would be prolonged in such weather before the onset of winter, when settlers and Indians generally ceased or curtailed hostilities. Another theory is that Indians merely prolonged their hunting in such weather in order to lay in more food for the winter. Before this American expression gained popularity in Britain during the mid to late 19th century, such weather in Britain was known as St Luke’s little summer or St Martin’s summer, their feast days Day falling on 18 October and 11 November respectively, but by the early 20th century at least these appellations had fallen away in favour of the American expression.