Support for a broken bone (6)
I believe the answer is:
splint
'support for a broken bone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for splint that I've seen before include "It's used to immobilise a broken limb" , "Aid to bone-setting" , "Straight object to keep bone in place" , "Bone setting support" , "It holds broken bones" .)