Head of state (5)
I believe the answer is:
ruler
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">head of state</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ruler that I've seen before include "Stationery item" , "Sovereign - support for a firm line!" , "Monarch or yardstick" , "Sovereign, for example" , "One who commands - often seen in the classroom" .)