Control or restrain (4)
I believe the answer is:
curb
I believe this is a double definition.
'control' is the first definition.
(I know that control can be written as curb)
'restrain' is the second definition.
(I know that curb is a type of restrain)
(Other definitions for curb that I've seen before include "Check or restrain" , "Rein in" , "Constrain" , "'Temper, hold in restraint (4)'" , "Strap used to restrain horse" .)