Top of vest opens forward, showing bust (9)
I believe the answer is:
insolvent
'bust' is the definition.
(I've seen this before)
'top of vest opens forward' is the wordplay.
'top of' says to take the initial letters.
'opens' means one lot of letters goes inside another (some letters open a gap in others).
'forward' becomes 'insolent' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'vest' is 'v'.
'v' going within 'insolent' is 'INSOLVENT'.
'showing' is the link.
Can you help me to learn more?
(Other definitions for insolvent that I've seen before include "on the rocks" , "Unable to pay debts owed" , "unable to raise the wind" , "In the red" , "Snivel not, although you are bankrupt!" .)