Fast-food chain with carhops (5)
I believe the answer is:
sonic
'fast-food chain with carhops' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sonic that I've seen before include "Relating to sound waves" , "Employing sound" , "Involving sound waves, say a boom" , "of noise" , "Relating to the speed of sound" .)