Border on which one is tense with anticipation (4)
I believe the answer is:
edge
'border' is the definition.
(I know that edge is a type of border)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for edge that I've seen before include "Move furtively; intense quality" , "Sharp ridge" , "Rim, lip" , "Sidle, lip" , "small advantage" .)