Corrupt act ended disastrously (8)
I believe the answer is:
decadent
'corrupt' is the definition.
(I've seen this before)
'act ended disastrously' is the wordplay.
'disastrously' indicates an anagram (I've seen this in other clues).
'act'+'ended'='actended'
'actended' is an anagram of 'DECADENT'.
(Other definitions for decadent that I've seen before include "Decanted in corrupt way" , "In moral or cultural decline" , "Self-indulgent or immoral" , "Dissolute and corrupt" , "Reflecting cultural decline" .)