Churchman's tackling complex issue that's neglected (7)
I believe the answer is:
disused
'that's neglected' is the definition.
(I've seen this before)
'churchman's tackling complex issue' is the wordplay.
'churchman' becomes 'dd'.
'tackling' is an insertion indicator (to tackle is to take possession of).
'complex' is an anagram indicator.
'issue' anagrammed gives 'isuse'.
'dd' enclosing 'isuse' is 'DISUSED'.
(Other definitions for disused that I've seen before include "Eg, like abandoned railways" , "No longer of service" , "empty" , "No longer observed or practised" , "No longer operated" .)