Depict pain that's mistreated and is reason for operation (12)
I believe the answer is:
appendicitis
'reason for operation' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'depict pain that's mistreated and is' is the wordplay.
'that's mistreated' is an anagram indicator.
'and' says to put letters next to each other.
'depict'+'pain'='depictpain'
'depictpain' with letters rearranged gives 'appendicit'.
'appendicit'+'is'='APPENDICITIS'
Can you help me to learn more?
(Other definitions for appendicitis that I've seen before include "Inflammation of abdominal sac" , "Inflammation for which operation may be needed" , "Painful inflammation" , "Inflammation of a sac attached to the large intestine" , "complaint" .)