reminder
/rɪˈmaɪndə(r)/noun
1- a thing that causes someone to remember something提醒物, 令人回忆的东西：
the watch tower is a reminder of the days when an enemy might appear at any moment.
岗楼使人们回忆起敌人随时可能会出现的那些日子。
1.1
- a message or communication designed to ensure that someone remembers something提示。
1.2
- a letter sent to remind someone of an obligation, especially to pay a bill催单, 催缴单。