Left on side of shelf (5)
I believe the answer is:
ledge
'shelf' is the definition.
(I know that shelf can be written as ledge)
'left on side' is the wordplay.
'left' becomes 'l' (common abbreviation).
'on' means one lot of letters go next to another.
'side' becomes 'edge' (edge is a kind of side).
'l'+'edge'='LEDGE'
'of' is the link.
(Other definitions for ledge that I've seen before include "Narrow shelf, often attached to window" , "Shelf-like projection" , "Projecting shelf, horizontal projection" , "Ridge or shelf" , "A step" .)