first day of autumn; beginning of fall
A poetic or traditional term for the first day of autumn, often used in haiku and seasonal contexts. In modern daily life, 秋の始まり or 立秋 are more common.
On the first day of autumn, you feel the coolness of the wind.
Compound of 秋 (autumn) + 立つ (to begin, to rise) + 日 (day). The exact historical derivation is uncertain, but it follows a classical pattern for naming seasonal turning points.