Ultimatum

The last proposition made in making a contract, a treaty, and the like; as, the government of the United States has given its ultimatum, has made the last proposition it will make to complete the proposed treaty. The word also means the result of a negotiation, and it comprises the final determination of the parties concerned in the object in dispute.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.