Discussed money for old instrument (4)
I believe the answer is:
lute
'old instrument' is the definition.
(I've seen this before)
'discussed money' is the wordplay.
'discussed' indicates a 'sounds like' (homophone) clue.
'money' becomes 'loot' (loot is a kind of money).
'loot' sounds like 'LUTE'.
'for' acts as a link.
(Other definitions for lute that I've seen before include "Ancient stringed instrument" , "Old musical instrument" , "Stringed instrument shaped like a halved egg" , "Protective packing" , "Plucked, pear-shaped instrument" .)