Shelf’s left corner (5)
I believe the answer is:
ledge
'shelf's' is the definition.
(synonyms)
'left corner' is the wordplay.
'left' becomes 'L' (common abbreviation).
'corner' becomes 'edge'.
'l'+'edge'='LEDGE'
(Other definitions for ledge that I've seen before include "Surface under e.g. window" , "A step" , "Ability to contain one's emotions" , "found halfway up a cliff?" , "Shelf-like projection" .)