Double quick and passing out (9)
I believe the answer is:
forthwith
'passing out' is the definition.
Both the answer and definition are adverbs. Perhaps there's an association between them I don't understand?
'double quick and' is the wordplay.
'double quick' becomes 'forth' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' becomes 'with'.
'forth'+'with'='FORTHWITH'
Can you help me to learn more?
(Other definitions for forthwith that I've seen before include "on the spot" , "Immediately as with froth" , "without further delay - at which it starts, audibly" , "Without delay or hesitation" .)