Church containing one clergyman (8)
I believe the answer is:
minister
'clergyman' is the definition.
(minister is a kind of clergyman)
'church containing one' is the wordplay.
'church' becomes 'minster' (minster is a kind of church).
'containing' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'minster' placed around 'i' is 'MINISTER'.
(Other definitions for minister that I've seen before include "Member of parliament" , "Attend to priest" , "Government or church officer" , "Member of the clergy or of the Front Bench" , "Tend" .)