Complaint about substance of policy (5)
I believe the answer is:
colic
'complaint' is the definition.
(medical complaint)
'about substance of policy' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'substance' becomes 'O' (O is an example).
'of policy' becomes 'lic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'c'+'o'+'lic'='COLIC'
Can you help me to learn more?
(Other definitions for colic that I've seen before include "gut reaction" , "Abdominal pain spasms" , "Severe abdominal pain" , "Briefly, officer in charge makes a complaint" , "Intestinal infection" .)