Four-wheeled vehicle (5)
'four-wheeled vehicle' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for car that I've seen before include "Railway carriage; vehicle" , "4-wheeled vehicle" , "estate, perhaps" , "Wheeled vehicle" , "Automobile" .)
(Other definitions for wagon that I've seen before include "Four-wheeled goods vehicle" , "Cart; rail truck" , "Horse-drawn vehicle" , "Wheeled vehicle drawn by a horse" , "Vehicle carrying goods" .)