Restrict, curb (5)
I believe the answer is:
limit
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">restrict</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that restrict is a more specific form of limit)</span><br/ ><br/ >'<span class="explanation-format__original">curb</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that curb is a more specific form of cumber)</span><br/ ><br/ ></span>
(Other definitions for limit that I've seen before include "Boundary or restriction" , "Boundary, demarcation line" , "Curtail" , "Utmost" , "Furthest point" .)