King Arthur's sword (9)
I believe the answer is:
excalibur
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">king arthur's sword</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 excalibur that I've seen before include "Legendary weapon" , "King Arthur's magic sword" , "King Arthur's magical sword" , "Traditional weapon" , "Steel flourished years ago" .)