Reason to restrict availability of alcohol (9)
I believe the answer is:
rationale
'reason' is the definition.
(I've seen this before)
'restrict availability of alcohol' is the wordplay.
'restrict' becomes 'ration' (rationing is a kind of restricting).
'availability of alcohol' becomes 'ale' (I can't justify this - if you can you should believe this answer much more).
'ration'+'ale'='RATIONALE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for rationale that I've seen before include "Logical reason for action" , "Motivation" , "Underlying principle" , "grounds?" , "Logical basis (for a course of action)" .)