Degenerate act ended badly (8)
I believe the answer is:
decadent
'degenerate' is the definition.
(thesaurus)
'act ended badly' is the wordplay.
'badly' indicates anagramming the letters.
'act'+'ended'='actended'
'actended' with letters rearranged gives 'DECADENT'.
(Other definitions for decadent that I've seen before include "Abandoning principles" , "Dissolute and corrupt" , "Debauched" , "Decanted in corrupt way" , "Luxuriously self-indulgent" .)