Shylock's business (5)
I believe the answer is:
usury
'shylock's business' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for usury that I've seen before include "Practice of loan sharks" , "Lending of money at exorbitant interest" , "Exorbitant or unlawful rate of interest" , "High-rate money lending" , "Taking excessive interest" .)