An ultimatum is a demand or statement that says "do this now or else something bad will happen." It's usually given by one person to another and has a strict deadline.
Think about it like being on a tightrope between two options. Someone might say, "Either you accept my offer for the house, or I'll sell it to someone else right away, which means you'll miss your chance to buy it." This kind of statement is an ultimatum because it forces the other person to make a decision quickly or face the consequences. It's often used in situations like business deals, politics, and even relationships when people feel they're at an impasse and need to force their way through.
(diplomacy) A final statement of terms or conditions made by one party to another, especially one that expresses a threat of reprisal or war if the terms are not met before some specified date and time.
Example: . . . But he was directed to present a memorial, urging many reasons for the restitution of the captures made before the war, to represent in its full force, the benefit that would arise, both to France and England, from the total desertion of the war in Germany, and if England should refuse the conditions, now offered as an ultimatum, to wait for farther instructions. The ultimatum arrived in London August 8. M. Buffy soon after wrote to Mr. Pitt, and in his answer, dated August 15, says, that, as to the stile of the ultimatum and letter, the king his master adheres both to the form and substance of them, he laments that peace appears by the proposals and conduct of France to be far distant, and retorts some charges and elusion and delay. M. Buffy, and Mr. Pitt however, had a conference on the two ultimatums jointly, and on the 30th of August an answer to the French ultimatum was delivered, in which the French propositions are agreed to, except in the following particulars. . .
