Clergyman is able to get no backing (5)
I believe the answer is:
canon
'clergyman' is the definition.
(canon is a kind of clergyman)
'able to get no backing' is the wordplay.
'able' becomes 'can'.
'to get' says to put letters next to each other.
'backing' says the letters should be written backwards.
'no' written backwards gives 'on'.
'can'+'on'='CANON'
'is' acts as a link.
(Other definitions for canon that I've seen before include "General rule; cleric" , "accepted criterion" , "Principle - church dignitary - regulation" , "General principle; musical round" , "Standard" .)