Hit the brakes (4)
I believe the answer is:
stop
'hit the brakes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stop that I've seen before include "Refrain from" , "Halt; finish" , "This watch is used to time races" , "Part of organ" , "Organ knob; get bus here" .)