Bone that parallels the radius (4)
I believe the answer is:
ulna
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bone that parallels the radius</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 ulna that I've seen before include "Bone from the human elbow" , "The longer and inner bone in forearm" , "Part of body" , "Thinner of two long bones in forearm" , "One in arms" .)