noun
first day of autumn; beginning of autumn
One of the 24 solar terms (二十四節気), marking the traditional start of autumn around August 7–8. Used in calendars and seasonal references.
See also: 二十四節気
今年の立秋は八月七日です。
This year, the first day of autumn is August 7th.
立秋を過ぎてもまだ暑い日が続いている。
Even after the beginning of autumn, the hot days continue.
From Chinese 立秋 (lìqiū), composed of 立 'to stand, to establish' and 秋 'autumn'. The term was adopted into Japanese as part of the traditional calendar system.