Most Reverend and cunning piece on board (10)
I believe the answer is:
archbishop
'most reverend' is the definition.
'archbishop' can be an answer for 'reverend' (archbishop is a kind of reverend). I'm not certain of the 'most' bit.
'cunning piece on board' is the wordplay.
'cunning' becomes 'arch' (arch can mean cunning or tricksy).
'piece on board' becomes 'bishop' (I can't justify this - if you can you should believe this answer much more).
'arch'+'bishop'='ARCHBISHOP'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for archbishop that I've seen before include "Senior churchman" , "ecclesiastical dignitary?" , "primate" , "Laud" , "Chief cleric" .)