Arrival or coming (6)
I believe the answer is:
advent
This clue is a double definition.
'arrival' is the first definition.
(advent is a kind of arrival)
'coming' is the second definition.
(advent is the arrival or coming of something)
(Other definitions for advent that I've seen before include "Arrival - time before Christmas" , "Pre-Christmas season for Christians" , "Christian season" , "observed by Christian church" , "approach" .)