Car; move quickly (5)
I believe the answer is:
motor
I believe this clue is a double definition.
'car' is the first definition.
(motor can informally mean a car)
'move quickly' is the second definition.
(I've seen this before)
(Other definitions for motor that I've seen before include "Car; travel quickly" , "Internal combustion engine" , "Move fast" , "Car - car's engine" , "(Transport using) engine" .)