Collision souvenir (4)
I believe the answer is:
dent
'collision souvenir' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dent that I've seen before include "Notch" , "tooth (13) [FRENCH]" , "Hollow, depression" , "Arthur, described by Douglas" , "Tend (anag.)" .)