The most common and most likely answer to this crossword clue is the 10 letter word PERCEPTION
I've seen this crossword clue in The Sunday Telegraph
P
E
R
C
E
P
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N
More clues leading to the result PERCEPTION
Buddy explains!
The straight part
We know that "Impression" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impression = perception.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PERCEPTION mean?
PERCEPTION noun- The organisation, identification and interpretation of sensory information.
- Conscious understanding of something.
- Vision (ability)
- Acuity
- (cognition) That which is detected by the five senses; not necessarily understood (imagine looking through fog, trying to understand if you see a small dog or a cat); also that which is detected within consciousness as a thought, intuition, deduction, etc.