High level of service provided (6)
I believe the answer is:
massif
'high level' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'service provided' is the wordplay.
'service' becomes 'mass' (mass is a church service).
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'mass'+'if'='MASSIF'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for massif that I've seen before include "Compact grouping of mountains" , "mountain peak" , "highlands" , "large amount of rock" , "Geological mountain formation" .)