One shouldn't trade in booze, reportedly (7)
I believe the answer is:
insider
'one shouldn't trade' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'in booze reportedly' is the wordplay.
'booze reportedly' becomes 'sider' (I can't explain this - if you can you should give a lot more credence to this answer).
'in'+'sider'='INSIDER'
Can you help me to learn more?
(Other definitions for insider that I've seen before include "One with privileged information" , "in prison?" , "Wrong sort of trading" , "Doing time, right, for this" , "One with special knowledge" .)