from morning till night; day and night; always
Literary or archaic expression for continuous effort or state throughout the day and night. In modern Japanese, 朝から晩まで or 日夜 are more common.
He devoted himself to his research day and night.
His tireless efforts, from morning till night, bore fruit.
Compound of 夙 (early morning) and 夜 (night), conveying the span from early morning to night. The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning 'day and night'.