The border route, possibly? (5)
I believe the answer is:
outer
'the border route possibly?' is the definition.
I can't judge whether this defines the answer.
'route possibly?' is the wordplay.
'possibly?' indicates anagramming the letters (I've seen 'possibly' mean this).
'route' anagrammed gives 'OUTER'.
Can you help me to learn more?
(Other definitions for outer that I've seen before include "Archer's shot" , "Route (anag.)" , "On the periphery" , "Outside; external" , "This space is beyond earth's atmosphere" .)