Levy on one vehicle (4)
I believe the answer is:
taxi
'vehicle' is the definition.
(I know that taxi is a type of motor car)
'levy on one' is the wordplay.
'levy' becomes 'tax' (taxing is a kind of levying).
'on' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'tax'+'i'='TAXI'
(Other definitions for taxi that I've seen before include "Minicab" , "(Plane) roll over tarmac" , "Motor vehicle for hire with driver" , "Motor-cab" , "Handgun" .)