IPA: /rɪˈmaɪndər/
KK: /rɪˈmaɪndər/
A person or thing that helps someone remember something.
I set a reminder on my phone to call my friend later.
Reminder → It is formed from "re-" (meaning again) and "mind" (from Old English "mynd", meaning memory or thought) and "-er" (meaning a person or thing that). The word "reminder" refers to something that causes one to remember again or brings back to mind.
Think of something that helps you remember 'again' ('re-') what you have in your 'memory' ('mind'). A reminder is something that brings back your thoughts.