- a period of mild, dry weather, usually accompanied by a hazy atmosphere, occurring usually in late October or early November and following a period of colder weather.
- a period of unusually settled warm weather after the end of summer proper
- a period of ease and tranquillity or of renewed productivity towards the end of a person’s life or of an epoch
“spell of warm weather after the first frost,” first recorded 1778, American English, perhaps so called because it was first noted in regions inhabited by Indians, or because the Indians first described it to the Europeans. No evidence connects it with the color of fall leaves or a season of Indian attacks on settlements. It is the American version of British All-Hallows summer, French été de la Saint-Martin (feast day Nov. 11), etc. Also colloquial was St. Luke’s summer (or little summer), period of warm weather occurring about St. Luke’s day (Oct. 18).
A period of unusually warm weather in the fall, often following a seasonable cold spell.
A period of mild, sunny weather occurring in late autumn, usually following a seasonable cold spell. For example, We had two whole days of Indian summer this year, and then it turned cold again. [Late 1700s]