Mix of alcohol in function before church (8)
I believe the answer is:
coalesce
'mix' is the definition.
(synonyms)
'alcohol in function before church' is the wordplay.
'alcohol' becomes 'ale' (ale is a kind of alcohol).
'in' means one lot of letters goes inside another.
'function' becomes 'cos' (mathematical function).
'before' says to put letters next to each other.
'church' becomes 'ce' (abbreviation for Church of England).
'ale' put within 'cos' is 'coales'.
'coales'+'ce'='COALESCE'
'of' acts as a link.
(Other definitions for coalesce that I've seen before include "Make one whole" , "Come together in one mass" , "Unite" , "Run together" , "To bring together" .)