Possibly arming at border (6)
I believe the answer is:
margin
'border' is the definition.
('margin' can be a synonym of 'border')
'possibly arming' is the wordplay.
'possibly' indicates an anagram.
'arming' with letters rearranged gives 'MARGIN'.
'at' acts as a link.
(Other definitions for margin that I've seen before include "Edge; room for error" , "Edge or space for error" , "Blank space around the edge" , "Border or leeway" , "Bound" .)