IOU noun 1phrase 1forms 1 noun1 •An informal promissory note that is not a negotiable instrument.When David couldn’t afford to match the money in the poker pot, he added an IOU for the remaining amount instead. phrase1 •I owe you.Customarily, if you borrow $10 for lunch from a coworker, writing IOU $10 on a yellow sticky note acts as a legal promissory note that you will repay said amount on payday. formsIOUs
