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during the night; at night
「夜中」 has other readings with different meanings.
夜中に一人で外出するのはとても危険だ。
Going out during the night is dangerous.
夜中に目が覚めることがよくある。
I often wake up during the night.
彼は試験前で夜中まで勉強をしている。
He studies during the night.