Reminder of a past event (7)
I believe the answer is:
memento
'reminder of a past event' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for memento that I've seen before include "trophy" , "Object kept as a souvenir" , "Souvenir, reminder of past event" , "A reminder of death - . . . . . . . mori" , "Keepsake or souvenir" .)