Old Russian ruler (4)
I believe the answer is:
tsar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">old russian ruler</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tsar that I've seen before include "Star for a Russian emperor" , "Russian monarch" , "Rats (anag)" , "Supremo" , "Absolute ruler" .)