Highland dagger (4)
I believe the answer is:
dirk
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">highland dagger</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 dirk that I've seen before include "Dagger (belonging to Bogarde?)" , "Highland dagger" , "Small dagger" , "Piercing instrument" , "Duncan's killer?" .)