Support for an injured arm (5)
I believe the answer is:
sling
'support for an injured arm' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sling that I've seen before include "Keeping afloat" , "shy" , "Sweetened drink with spirit base" , "Chuck; support for damaged arm" , "harness for broken arm" .)