Curtail, curb (8)
I believe the answer is:
restrict
I believe this clue is a double definition.
'curtail' is the first definition.
(I know that curtail can be written as restrict)
'curb' is the second definition.
(I know that curb can be written as restrict)
(Other definitions for restrict that I've seen before include "Place limit on" , "'Restrain, limit (8)'" , "Place limits on" , "Deprive of freedom" , "Keep within bounds" .)