Dupe old man with hint of nonchalance (4)
I believe the answer is:
pawn
'dupe' is the definition.
(I've seen this in another clue)
'old man with hint of nonchalance' is the wordplay.
'old man' becomes 'pa' (both can mean someone's father).
'with' becomes 'w' (abbreviation).
'hint of' suggests taking the first letters (the smallest possible amount of the word).
The first letter of 'nonchalance' is 'n'.
'pa'+'w'+'n'='PAWN'
(Other definitions for pawn that I've seen before include "Minor chess piece" , "Man of lowest value" , "one used by another" , "Part with temporarily to raise money" , "Insignificant player" .)