Social event or sexual relationship (6)
I believe the answer is:
affair
This clue is a double definition.
'social event' is the first definition.
(affair is a kind of social event)
'sexual relationship' is the second definition.
(affair is a kind of sexual relationship)
(Other definitions for affair that I've seen before include "Secret romance" , "A matter; amorous episode" , "Liaison or intrigue" , "Thing to be done with raffia" , "River dam" .)