Commercial opening is coming (6)
I believe the answer is:
advent
'is coming' is the definition.
(I've seen this before)
'commercial opening' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'opening' becomes 'vent' (vent is a kind of opening).
'ad'+'vent'='ADVENT'
(Other definitions for advent that I've seen before include "Arrival - time before Christmas" , "Pre-Christmas period" , "Christian season" , "It's a-coming in December!" , "Arrival of important person or event" .)