Promissory notes are a common financial instrument that people often use when borrowing or lending money. These are legal documents that promise repayment of a specified amount at a certain time. While the term "promissory note" is well-known, there are several synonyms that can be used to describe this type of financial instrument. Some of these include IOU, promise to pay, bond, debenture, note, and certificate of indebtedness. Each of these terms describes a similar financial agreement between two parties, with a promise of repayment in the future. Regardless of the term used, promissory notes are a crucial financial tool for many businesses and individuals.