reminder
nounUK /rɪˈmaɪn.dər/
US /rɪˈmaɪn.dɚ/
Something that helps you remember to do something.
I set a reminder on my phone to call Grandma.
OTHER MEANINGS
2. A message or note that helps someone remember an event or task.
The teacher sent a reminder about the field trip.
3. Something that makes you think of something else again.
The old song was a reminder of summer camp.
4. A formal letter telling someone to pay or do something.
The bank sent a reminder about the late payment.