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An abbreviation of "I owe you," with "owe" and "you" represented by the letters O and U, respectively.
1. A written promise to pay an outstanding debt. A: "My brother wants to borrow some money." B: "No way! I still have the IOU he gave me for the $500 I lent him last year!" She took $20 out of her dad's wallet and replaced it with a scrap of paper that had "IOU" scribbled on it.
2. Used to express that one is indebted to someone for some favor or kindness. A: "Can I borrow your car for the weekend?" B: "Sure, no problem." A: "Thanks, dude. IOU."
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.