Cross endless borders from elsewhere (8)
I believe the answer is:
external
'from elsewhere' is the definition.
(from outside)
'cross endless borders' is the wordplay.
'cross' becomes 'x' (X is cross-shaped).
'endless' becomes 'eternal' (I've seen this before).
'borders' indicates putting letters inside.
'x' going into 'eternal' is 'EXTERNAL'.
(Other definitions for external that I've seen before include "Belonging to the outside" , "Surface" , "involving foreign nations" , "Superficial" , "Relating to the outside" .)