Decomposed (6)
I believe the answer is:
rotten
'decomposed' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for rotten that I've seen before include "'Decayed, stinking (6)'" , "Decayed or detestable" , "Morally despicable" , "Decaying or morally corrupt" , "Corrupt; very bad" .)