From The Collaborative International Dictionary of English v.0.48 [gcide]:
1. A final proposition, concession, or condition; especially, the final propositions, conditions, or terms, offered by either of the parties in a diplomatic negotiation; the most favorable terms that a negotiator can offer, the rejection of which usually puts an end to the hesitation.
2. A final demand, the rejection of which may lead to a resort to force or other compelling action by the party presenting the ultimatum. In international diplomacy, an ultimatum may be used as by the demanding country as a signal to other countries that it gave the other country a seemingly reasonable opportunity to avoid a war; in this way, the demanding country may seek to avoid responsibility for starting a war. [PJC]
From WordNet (r) 3.0 (2006) [wn]:
http://www.define.com is a PRIVATE SECTOR EDUCATIONAL NONPROFIT TERRESTRIAL ALIEN BLOG that PROMOTES FUTURISTIC SECULARISM, WORLDWIDE ELECTRONIC DEMOCRACY, OPEN and TRANSPARENT GOVERNMENT and WORLDWIDE BANKING REFORM. THIS IS COMPUTER-AIDED PEACE ON EARTH. COMPUTERS WILL PAY FOR EVERYTHING. PEOPLE DO NOT NEED MONEY.
www.FreeWorldBank.org on Amazon S3
Eye and Pyramid BANKING REFORM CHALLENGE