Returning in dream, similar doctrine (3)
I believe the answer is:
ism
'doctrine' is the definition.
(suffix for disciplines or schools of thought)
'returning in dream similar' is the wordplay.
'returning' says the letters should be written backwards.
'in' says the answer is hidden in the clue.
'msi' can be found hidden inside 'dream similar'.
'msi' in reverse letter order is 'ISM'.
(Other definitions for ism that I've seen before include "Ideological movement" , "Informal doctrine found in Bismarck" , "Suffix denoting doctrine or practice" , "Informal doctrine - any one" , "Any doctrine or theory" .)