Restrict, curb (5)
I believe the answer is:
limit
I believe this is a double definition.
'restrict' is the first definition.
(I know that restrict is a more specific form of limit)
'curb' is the second definition.
(I know that curb is a more specific form of cumber)
(Other definitions for limit that I've seen before include "Boundary or restriction" , "Boundary, demarcation line" , "Curtail" , "Utmost" , "Furthest point" .)