Meet a number on the border (8)
I believe the answer is:
converge
'meet' is the definition.
(converging is a kind of meeting)
'a number on the border' is the wordplay.
'a number on' becomes 'con' (I can't explain this - if you can you should believe this answer much more).
'the border' becomes 'verge' (verge is a kind of border).
'con'+'verge'='CONVERGE'
Can you help me to learn more?
(Other definitions for converge that I've seen before include "fuse" , "Move toward the same point" , "Tend to meet at a point" , "Approach a single point" , "tend to get together" .)