The initial, introductory evaluation upon meeting a person, encountering something, or experiencing a situation for the first time. I had a bad first impression of the job when, on my very first day, the boss humiliated me in front of everyone in the office. I didn't have a great first impression of Steve, but we ended up becoming very close friends.

To be living, operating, or functioning with the belief that something is true. Jeremy's always been under the impression that he's a great writer, even though he's never written more than a few crummy poems. Oh, I was under the impression that we were meeting at two—did that change?

To have or create a strong impact on someone, whether good or bad (usually specified by an adjective before "impression.") Make sure you brush your hair and wear a clean suit—you want to make a good impression on your first day in the office. It's clear that the defendant's impassioned speech made a strong impression on the jury.

Holding the assumption or belief (that something is true). Oh, sorry, I was under the impression that you two were a couple. My mistake. A: "Aren't you planning on retiring soon?" B: "Why would you be under that impression?"

To have or create a strong impact on someone, whether good or bad (usually specified by an adjective before "impression.") Make sure you brush your hair and wear a clean suit—you want to leave a good impression on your first day in the office. It's clear that the defendant's impassioned speech left a strong impression on the jury.

People are most apt to remember the initial, introductory evaluation upon meeting a person, encountering something, or experiencing a situation for the first time. It took a while for the two of us to become friends because I didn't have a great first impression of him, and first impressions are the most lasting. Ugh, asparagus just repulses me. The first time I ever had it, it was mushy and gross—further evidence that first impressions are the most lasting.