Crossword Genius

Twelve, a large crowd for this celebration (8,4)

Ross

I believe the answer is:

midnight mass

'this celebration' is the definition.
(type of religious celebration)

'twelve a large crowd' is the wordplay.
'twelve' becomes 'midnight' (I've seen this before).
'a large crowd' becomes 'mass' (a mass of people).
'midnight'+'mass'='MIDNIGHT MASS'

'for' acts as a link.

(Another definition for midnight mass that I've seen is " church service".)

I've seen this clue in The Times.
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