promissory note

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A negotiable written promise to pay a specified sum of money on demand or at a particular time.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun finance A document saying that someone owes a specific amount of money to someone else, often with the deadline and interest fees.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a promise to pay a specified amount on demand or at a certain time