Restriction; boundary (5)
I believe the answer is:
limit
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">restriction</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">boundary</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that boundary can be written as limit)</span><br/ ><br/ ></span>
(Other definitions for limit that I've seen before include "Boundary or restriction" , "maximum number" , "Keep in" , "border" , "Extreme point" .)