reminder

The accident was a sobering reminder of the dangers of climbing.这场事故是一个发人深省的警示，提醒人们登山有危险。

a constant reminder of his past经常勾起他回忆的东西

She sent him an e-mail reminder about the meeting.她给他发了一封电子邮件，提醒他开会。

I wrote myself a reminder to take out the trash.我写了个纸条，提醒自己倒垃圾。