Bone in the forearm (4)
I believe the answer is:
ulna
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bone in the forearm</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 ulna that I've seen before include "Bone from the human elbow" , "Radius partner" , "Part of body" , "part of anatomy" , "Inner bone of the human forearm" .)