Break . . . or brake (4)
I believe the answer is:
stop
I believe this is a double definition.
'break' is the first definition.
(both can mean to malfunction or stop working)
'brake' is the second definition.
(I've seen this in another clue)
(Other definitions for stop that I've seen before include "Standstill" , "Check" , "Prevent - desist" , "Intercept" , "End - period" .)