Fifty-fifty odds on getting good service (8)
I believe the answer is:
evensong
'service' is the definition.
(type of church service)
'fifty-fifty odds on getting good' is the wordplay.
'fifty-fifty odds' becomes 'evens' (betting term).
'getting' is a charade indicator (letters next to each other).
'good' becomes 'g' (abbreviation).
'evens'+'on'+'g'='EVENSONG'
(Other definitions for evensong that I've seen before include "... Prayers" , "Anglican service" , "Service of evening prayer in Church of England" , "Church service late in the day" , "6 [SERVICE] ?" .)