Evil church about to be honest (7)
I believe the answer is:
sincere
'honest' is the definition.
(similar in meaning)
'evil church about' is the wordplay.
'evil' becomes 'sin' (synonyms).
'church' becomes 'CE' (abbreviation for Church of England).
'about' becomes 're' ('re' means regarding or about).
'sin'+'ce'+'re'='SINCERE'
'to be' acts as a link.
(Other definitions for sincere that I've seen before include "like informal correspondents?" , "Genuine and honest" , "'Genuine, not deceitful (7)'" , "natural?" , "True" .)