Sleeve filler (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sleeve filler</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 arm that I've seen before include "ready for war" , "Accoutre" , "strip of land?" , "Human limb" , "One fired" .)