An ultimatum is a warning to someone that unless they act in a particular way, action will be taken against them. They issued an ultimatum to the police to rid an area of racist attackers, or they will take the law into their own hands. ultimatums ultimata a threat saying that if someone does not do what you want by a particular time, you will do something to punish them
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 a negotiator can offer, the rejection of which usually puts an end to the hesitation