Mistreat vehicle in unoccupied aerodrome (5)
I believe the answer is:
abuse
'mistreat' is the definition.
(synonyms)
'vehicle in unoccupied aerodrome' is the wordplay.
'vehicle' becomes 'bus' (public transport vehicle).
'in' indicates putting letters inside.
'unoccupied' says to hollow out the word (remove centre letters) (remove the inside letters which occupy the word).
'aerodrome' with its middle removed is 'ae'.
'bus' put inside 'ae' is 'ABUSE'.
(Other definitions for abuse that I've seen before include "Berate - exploitation" , "Cruel treatment" , "Insulting language" , "Treat with cruelty" , "Castigate" .)