Abdicator of 1917 (4)
I believe the answer is:
tsar
'abdicator of 1917' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tsar that I've seen before include "Powerful man" , "Title of Russian emperor" , "Supreme authority" , "Star for a Russian emperor" , "Male monarch" .)