an experience that causes you to remember something
"The smell of fresh rain served as a reminder of our childhood summers spent playing in puddles."
someone who gives a warning so that a mistake can be avoided
"The safety inspector acted as a reminder to wear helmets, ensuring no accidents occurred on the construction site."
Someone or something that reminds.
"The flashing red light served as a constant reminder to check the fuel gauge before driving far from home."
In plain English: A reminder is something that makes you remember to do or think about something important later.
"The sticky note on my fridge was just a gentle reminder to buy milk."
The word reminder is formed by adding the suffix -er to the verb remind. It was first used to describe a person or thing that causes someone to remember something.