Border, limit (8)
I believe the answer is:
boundary
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">border</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that border can be written as boundary)</span><br/ ><br/ >'<span class="explanation-format__original">limit</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for boundary that I've seen before include "Line determining the limits of an area" , "Four, perhaps" , "Perimeter: demarcation" , "Limit (of an area)" , "4 possibly" .)