Dress put on mature bull (7)
'bull' is the definition.
(both can mean nonsense or lies)
'dress put on mature' is the wordplay.
'dress' becomes 'garb' (synonyms).
'put on' is a charade indicator (letters next to each other).
'mature' becomes 'age' (synonyms).
(Other definitions for garbage that I've seen before include "hot air", "US rubbish", "Food waste or trash", "Refuse - worthless talk", "Pop group; rubbish".)