Disappointment ain't turned about by acquiring capital (10)
I believe the answer is:
anticlimax
'disappointment' is the definition.
(I've seen this before)
'ain't turned about by acquiring capital' is the wordplay.
'turned' indicates anagramming the letters.
'about by acquiring capital' becomes 'climax' (I can't justify this - if you can you should give a lot more credence to this answer).
'aint' is an anagram of 'anti'.
'anti'+'climax'='ANTICLIMAX'
Can you help me to learn more?
(Other definitions for anticlimax that I've seen before include "Let-down after excitement" , "Damp squib" , "Disappointing ending" , "disappointment" , "disappointing outcome" .)