(The). The autumnal summer; generally the finest and mildest part of the whole year, especially in North America.
“The gilding of the Indian summer mellowed the pastures far and wide.
The russet woods stood ripe to be stript, but were yet full of leaf.
The purple of heath-bloom, faded but not withered, tinged the bills
... Fieldhead gardens bore the seal of gentle decay; ... its time of
flowers and even of fruit was over.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894