Occurrence, a happening (5)
I believe the answer is:
event
This clue is a double definition.
'occurrence' is the first definition.
(I've seen this before)
'a happening' is the second definition.
(I've seen this before)
(Other definitions for event that I've seen before include "tournament" , "Episode" , "Happening, incident" , "heat, perhaps" , "case" .)