Constrain, limit (4)
I believe the answer is:
curb
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">constrain</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(curbing is a kind of constraining)</span><br/ ><br/ >'<span class="explanation-format__original">limit</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 curb that I've seen before include "[LIMITATION]" , "Rein in" , "Muzzle" , "'Temper, hold in restraint (4)'" , "Check or restrain" .)