Church assembly engaged in controversy, no doubt (5)
I believe the answer is:
synod
'church assembly' is the definition.
(I've seen this before)
'engaged in controversy no doubt' is the wordplay.
'engaged in' indicates the answer is hidden within the clue.
'SYNOD' is hidden within 'controversy no doubt'.
(Other definitions for synod that I've seen before include "group of clergymen" , "council meeting" , "Ecclesiastical council" , "Ecclesiastic council" , "Church assembly" .)