A rave at back of room where wine is kept (9)
I believe the answer is:
cellarage
'where wine is kept' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'a rave at back of room' is the wordplay.
'a rave' becomes 'age' (I can't justify this - if you can you should give a lot more credence to this answer).
'at back of' says to put letters next to each other.
'room' becomes 'cellar' (I've seen this before).
'age' put after 'cellar' is 'CELLARAGE'.
Can you help me to learn more?
(Other definitions for cellarage that I've seen before include "payment for port's security?" , "Charge for storing (wine?)" , "Cost of storing wine" , "Stores" .)