promissory note pro·mis·so·rynote uncommon noun 1. a promise to pay a specified amount on demand or at a certain time “I had to co-sign his note at the bank” Synonymsnotepromissory notenote of hand Related words Broader terms debt instrument Narrower terms demand notenote receivablenote payablemunicipal noteIOUtime note WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.