the day before or the previous day
(as noun)前一天
The day before had been an exceptionally busy one.前一天是极度忙碌的一天。
All memory of the previous day seemed to have been wiped from Lavinia's mind.有关前一天的所有记忆似乎都已经从拉维妮娅的脑海中抹去了。
(as adverb)在前一天
It had all started to go wrong the day before.从前一天开始一切都变得不正常。
The letter had been delivered the previous day.那封信在前一天就送到了。