Old Japanese assassin (5)
I believe the answer is:
ninja
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">old japanese assassin</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 ninja that I've seen before include "Person skilled in Japanese martial art" , "agent from the east" , "Stealthy Japanese fighter" , "Japanese expert in stealth and martial arts" , "Japanese trained assassin" .)