Emperor (4)
I believe the answer is:
tsar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">emperor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tsar that I've seen before include "Tyrant" , "Word derived from Caesar, used by European rulers since 1547" , "Despot" , "Nicholas II, say" , "Eg, Ivan the Terrible" .)