Commercial outlet that is coming (6)
I believe the answer is:
advent
'coming' is the definition.
('advent' can be a synonym of 'coming')
'commercial outlet' is the wordplay.
'commercial' becomes 'ad'.
'outlet' becomes 'vent' (I've seen this before).
'ad'+'vent'='ADVENT'
'that is' acts as a link.
(Other definitions for advent that I've seen before include "Second Coming" , "Pre-Christmas period" , "sort of calendar" , "Season preceding Christmas" , "appearance" .)