Big impression (6)
I believe the answer is:
splash
'big impression' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for splash that I've seen before include "Spend freely or make wet" , "Noise of a body falling into water" , "Cause water to fly about, make wet" , "Sound of an object hitting liquid" , "Dash with liquid" .)