One who takes great interest in business (6)
I believe the answer is:
usurer
'one who takes great interest in business' is the definition.
(usury is lending money with very high interest)
This is the entire clue.
(Other definitions for usurer that I've seen before include "One who exacts much interest on loans." , "Person who charges excessive interest on loan" , "Unscrupulous lender" , "Lender who charges exorbitant interest rates" , "Moneylender who charges excessive rates of interest" .)