Flexible sword (4)

I believe the answer is:
foil
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flexible sword</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for foil that I've seen before include "Leaf of metal" , "Food kept fresh in this" , "Queer" , "Frustrate; kitchen wrap" , "Thwart - contrasting thing - sword" .)