A Charlie, clergyman is faithful (8)
I believe the answer is:
accurate
'faithful' is the definition.
(similar in meaning)
'a charlie clergyman' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet).
'clergyman' becomes 'curate' (assistant to a priest).
'a'+'c'+'curate'='ACCURATE'
'is' is the link.
(Other definitions for accurate that I've seen before include "carefully and precisely" , "Correct in all details" , "Absolutely correct" , "not deviating from the truth?" , "True!" .)