A church service (3)
I believe the answer is:
ace
'service' is the definition.
(I've seen this before)
'a church' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England**).
'a'+'ce'='ACE'
(Other definitions for ace that I've seen before include "The opponent can't return this serve" , "Adept" , "Very good; playing card" , "Expert; one" , "Player who excels" .)