Broker fast investing with silver (4,5)
I believe the answer is:
land agent
'broker' is the definition.
(land agent is a kind of broker)
'fast investing with silver' is the wordplay.
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'investing' means one lot of letters goes inside another (inserted letters are taken in or invested).
'with' becomes 'and'.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'and'+'ag'='andag'
'lent' placed around 'andag' is 'LAND-AGENT'.
(Other definitions for land agent that I've seen before include "Estate steward" , "Estate manager" , "Scots factor" .)