The most common and most likely answer to this crossword clue is the 9 letter word FOOTSTEPS
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Buddy explains!

The straight part
We know that "impressions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impressions = footsteps.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 FOOTSTEPS mean?
FOOTSTEPS noun- The mark or impression left by a foot; a track.
- By extension, the indications or waypoints of a course or direction taken.
- The sound made by walking, running etc.
- A step, as in a stair.
- The distance between one foot and the next when walking; a pace.
- The act of taking a step.
- An inclined plane under a hand printing press.