Cross to miss a Christmas carol gathering (8)
I believe the answer is:
amassing
'gathering' is the definition.
('amass' can be a synonym of 'gather')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for amassing that I've seen before include "Putting together" , "Accumulating a large amount" , "Building up (a stock)" , "Accumulating in quantity" , "Making a collection of" .)