Driver (9)
'driver' is the definition.
(motorist is a kind of driver)
This is all the clue.
(Other definitions for motorist that I've seen before include "One relying on car" , "One driving" , "Traveller" , "One drives" , "One on the road" .)
'driver' is the definition.
(chauffeur is a kind of driver)
This is the entire clue.
(Other definitions for chauffeur that I've seen before include "One employed to drive a car for someone" , "Personal driver" , "Professional driver" , "Driver for private car" , "Person employed to drive a car" .)