In which, drunk on the hard stuff, one's very merry (4,7)
I believe the answer is:
high spirits
'in which drunk on the hard stuff one's very merry' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'in which drunk on' is the wordplay.
'in which' becomes 'spirits' (I can't justify this - if you can you should believe this answer much more).
'drunk' becomes 'high' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'spirits' after 'high' is 'HIGH SPIRITS'.
Can you help me to learn more?
(Other definitions for high spirits that I've seen before include "Elated frame of mind" , "Cheerful mood" .)