An example of prompt is when you whisper a line to an actor who forgot what to say next.
An example of prompt is an event that starts an argument.
An example of prompt is someone who is told to arrive at 7:00 and who gets there at 7:00.
A prompt reply.
I prompted him to get a new job.
If he forgets his words I will prompt him.
A noise prompted the guard to go back and investigate.
The accident prompted a review of school safety policy.
I filled in my name where the prompt appeared on the computer screen but my account wasn't recognized.
Origin of prompt
From American Heritage Dictionary of the English Language, 5th Edition