Cheapskate's letters

• Letters written by someone who's a bit shy?
• Evidence of debt
• Red letters?
• Slip about money
• Promise to repay, for short
• Debt voucher
• Representing
• Gambler's debt, so to speak
• Pay-you-later kin

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
I O U \I O U\, IOU \I.O.U\([imac]" [=o]" [=u]"). [phonetic, from I owe you.] A paper having on it these letters, with a sum named, and duly signed; -- in use in England as an acknowledgment of a debt, and taken as evidence thereof, but not amounting to ...