1488: Why Money is 'Notes' Jan 8, 2019

Before there was fully fledged paper money but after people realized that carrying large amounts of gold and silver around was impractical, individual banks would give out notes—essentially like a check or an I.O.U.—that were redeemable at the banks themselves for a specified amount of, usually, gold. These notes were called 'promissory notes', and even though major economies moved off of a gold standard years ago, the term 'note' stuck. In Scotland however, printed bills are still only promissory notes, and are not legal tender even in Scotland.
For more on how things came to be, watch How Writing Began