Cars (6)
'cars' is the definition.
('auto' can be a synonym of 'car')
This is all the clue.
(Other definitions for autos that I've seen before include "Cars" , "Freeway traffic" , "Religious dramas" .)
(Other definitions for motors that I've seen before include "They supply motion or power" , "Drives" , "shifts" , "Locomotives, machines" , "Engines" .)