Bone near the radius (4)
I believe the answer is:
ulna
'bone near the radius' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ulna that I've seen before include "The longer and inner bone in forearm" , "Thinner and longer of two bones in forearm" , "One in arms" , "Radius partner" , "Part of bone-structure" .)