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9th day of the month
nine days
9日に届けを出した。
I submitted the form on the 9th.
来月の9日に歯医者の予約がある。
I have a dentist appointment on the 9th of next month.
9日までに宿題を出さなくてはいけないそうです。
Apparently the homework has to be submitted by the 9th.