Proper to put notes with coin (6)
I believe the answer is:
decent
'proper' is the definition.
(similar in meaning)
'notes with coin' is the wordplay.
'notes' becomes 'de' (two musical notes).
'with' means one lot of letters go next to another.
'coin' becomes 'cent' (cent is a kind of coin).
'de'+'cent'='DECENT'
'to put' is the link.
(Other definitions for decent that I've seen before include "reasonable" , "Proper; passable" , "Proper and suitable" , "Respectable; satisfactory" , "Polite - fitting" .)