Strip to support and immobilise a broken bone (6)
I believe the answer is:
splint
'strip to support and immobilise a broken bone' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for splint that I've seen before include "Support for injured arm" , "Aid to bone-setting" , "Firelighter" , "Contrivance for holding a broken bone in position" , "Piece or rigid material to secure broken bone" .)