Really impress (3)
I believe the answer is:
awe
'really impress' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for awe that I've seen before include "viewed with apprehension" , "Fear; reverence" , "Reverent fear" , "Scots lock [LOCH??]" , "Reverential respect" .)