Left on border of shelf (5)
I believe the answer is:
ledge
'shelf' is the definition.
('ledge' can be a synonym of 'shelf')
'left on border' is the wordplay.
'left' becomes 'l' (common abbreviation).
'on' is a charade indicator (letters next to each other).
'border' becomes 'edge' ('edge' can be a synonym of 'border').
'l'+'edge'='LEDGE'
'of' acts as a link.
(Other definitions for ledge that I've seen before include "Shelf-like projection" , "found halfway up a cliff?" , "Narrow shelf, often attached to window" , "rocky situation?" , "Shelf-life projection" .)