Friend left by old man (3)
I believe the answer is:
pal
'friend' is the definition.
(pal can mean a friend)
'left by old man' is the wordplay.
'left' becomes 'l' (common abbreviation).
'by' says to put letters next to each other.
'old man' becomes 'pa' (both can mean someone's father).
'l' put after 'pa' is 'PAL'.
(Other definitions for pal that I've seen before include "Bud" , "Crony" , "Buddy, chum" , "Friend (colloq.)" , "China" .)