Arm support (5)
I believe the answer is:
sling
'arm support' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sling that I've seen before include "Support bandage; drink" , "Stone-throwing weapon" , "Catapult or support as for injured arm" , "Primitive weapon" , "Keeping afloat" .)