Sturdy vehicle covered in rubbish (6)
I believe the answer is:
robust
'sturdy' is the definition.
(similar in meaning)
'vehicle covered in rubbish' is the wordplay.
'vehicle' becomes 'bus' (public transport vehicle).
'covered in' means one lot of letters goes inside another.
'rubbish' becomes 'rot' (both can mean nonsense).
'bus' inserted inside 'rot' is 'ROBUST'.
(Other definitions for robust that I've seen before include "Study and durable" , "Sturdy, resilient" , "Vigorous and hearty" , "Forceful" , "Athletic" .)