Proper to put keys next to coin (6)
I believe the answer is:
decent
'proper' is the definition.
(associated in meaning)
'keys next to coin' is the wordplay.
'keys' becomes 'de' (I've seen this in other clues).
'next to' says to put letters next to each other.
'coin' becomes 'cent' (cent is a kind of coin).
'de'+'cent'='DECENT'
'to put' acts as a link.
(Other definitions for decent that I've seen before include "Honest and modest" , "Appropriate, fitting" , "Generally acceptable" , "Generous or modest" , "Seemly, respectable" .)