Bust is forward maintaining volume (9)
I believe the answer is:
insolvent
'bust' is the definition.
(I've seen this before)
'forward maintaining volume' is the wordplay.
'forward' becomes 'insolent' (I can't explain this - if you can you should give a lot more credence to this answer).
'maintaining' indicates putting letters inside (inserted letters are held or maintained).
'volume' becomes 'v' (abbreviation for volume in book titles).
'insolent' going around 'v' is 'INSOLVENT'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for insolvent that I've seen before include "Snivel not, although you are bankrupt!" , "deep in debt?" , "Gone bust, without a bean" , "without the means to pay" , "Broke" .)