Possibly arming at the border (6)
I believe the answer is:
margin
'the border' is the definition.
('margin' can be a synonym of 'border')
'possibly arming' is the wordplay.
'possibly' indicates anagramming the letters.
'arming' is an anagram of 'MARGIN'.
'at' is the link.
(Other definitions for margin that I've seen before include "Blank space around a text" , "Bound" , "Edge or space for error" , "bank" , "Periphery" .)