Ruler returning prohibits any dissent? Not entirely (6)
I believe the answer is:
dynast
'ruler' is the definition.
(dynast is a kind of ruler)
'returning prohibits any dissent? not entirely' is the wordplay.
'returning' is a reversal indicator.
'not entirely' indicates the answer is hidden within the clue.
'tsanyd' can be found hidden inside 'prohibits any dissent'.
'tsanyd' written backwards gives 'DYNAST'.
(Other definitions for dynast that I've seen before include "Member of a hereditary ruling family" , "One ruling" , "Powerful hereditary ruler" .)