If you are under the impression that something is the case, you believe that it is the case, usually when it is not actually the case. He had apparently been under the impression that a military coup was in progress.

What does was under the impression mean?

Definition of be under the impression

: to have an idea or belief that is usually not clear or certain I was under the impression that admission was free.

How do you use impression in a sentence?

Examples of impression in a Sentence

First impressions are important but can be misleading. In her journal, she recorded her impressions of the city. Her kindness left a lasting impression on her students. I got the distinct impression that they didn't mean to stay long.