A cut arm: it might turn out so? (9)
I believe the answer is:
traumatic
'out so?' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I can't see?
'a cut arm it might turn' is the wordplay.
'a cut arm it' can be anagrammed to 'TRAUMATIC'.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for traumatic that I've seen before include "Psychologically painful" , "Direly shocking" , "Psychologically damaging" , "Deeply disturbing" , "Deeply distressing" .)