Border, limit (8)
I believe the answer is:
boundary
I believe this is a double definition.
'border' is the first definition.
(I know that border can be written as boundary)
'limit' is the second definition.
(synonyms)
(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" .)