Dictator's criminal conspirator (5)
I believe the answer is:
cinna
'conspirator' is the definition.
(I've seen this before)
'dictator's criminal' is the wordplay.
'dictator's' shows a homophone (sound like) (as somebody dictating would pronounce the word).
'criminal' becomes 'sinner' (someone who has done bad deeds).
'sinner' is a homophone of 'CINNA'.
(Other definitions for cinna that I've seen before include "Roman consul" , "Plotter in 'Julius Caesar'" , "Conspirator against Caesar" , "conspirator in Rome" , "Poet" .)