Bad actor, trashed, promises to return ready (9)
I believe the answer is:
atrocious
'bad' is the definition.
(similar in meaning)
'actor trashed promises to return ready' is the wordplay.
'trashed' indicates an anagram.
'promises to return ready' becomes 'ious' (an IOU is a promise to return money ie 'ready').
'actor' is an anagram of 'atroc'.
'atroc'+'ious'='ATROCIOUS'
(Other definitions for atrocious that I've seen before include "Terrible" , "Extremely bad" , "Appalling" , "Extremely wicked" , "Horrifying" .)