Sign of healing (4)
I believe the answer is:
scab
'sign of healing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scab that I've seen before include "despicable person" , "he refuses to come out" , "work when others are out" , "Evidence of healing wound - crosser of picket line" , "Disease of sheep" .)