1. 〔昼も夜も〕day and night;〔常に〕always, constantly
    • 彼は日夜勉強している
    • He studies day and night.
    • 地震に備えて日夜警戒態勢をとっている
    • They are constantly [always] on the alert for an earthquake.
    • 鉄道の復旧作業に日夜つとめた
    • They worked around the clock to reopen the railroad.