Account by clergyman for faithful (8)
I believe the answer is:
accurate
'faithful' is the definition.
('accurate' can be similar in meaning to 'faithful')
'account by clergyman' is the wordplay.
'account' becomes 'ac'.
'by' is a charade indicator (letters next to each other).
'clergyman' becomes 'curate' (curate is a kind of clergyman**).
'ac'+'curate'='ACCURATE'
'for' acts as a link.
(Other definitions for accurate that I've seen before include "Careful, precise" , "telling it like it is" , "Exactly right" , "True!" , "Precise, correct" .)