usury

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The practice of lending money and charging the borrower interest, especially at an exorbitant or illegally high rate.
• noun An excessive or illegally high rate of interest charged on borrowed money.
• noun Archaic Interest charged or paid on a loan.

from The Century Dictionary.

• noun Originally, any premium paid, or stipulated to be paid, for the use of money; interest. [Obsolete or archaic.]
• noun An excessive or inordinate premium paid, or stipulated to be paid, for the use of money borrowed; any such premium in excess of the rate established or permitted by law, which varies locally.
• noun The practice of lending money at interest, or of taking interest for money lent; specifically, and now almost exclusively, the practice of taking exorbitant or excessive interest; the taking of extortionate interest from the needy or extravagant.

from the GNU version of the Collaborative International Dictionary of English.

• noun Obs. or Archaic A premium or increase paid, or stipulated to be paid, for a loan, as of money; interest.
• noun obsolete The practice of taking interest.
• noun (Law) Interest in excess of a legal rate charged to a borrower for the use of money.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable An exorbitant rate of interest, in excess of any legal rates or at least immorally.
• noun uncountable The practice of lending money at such rates.
• noun uncountable, archaic The practice of lending money at interest.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an exorbitant or unlawful rate of interest
• noun the act of lending money at an exorbitant rate of interest