a threat in which a person or group of people are warned that if they do not do a particular thing, something unpleasant will happen to them. It is usually the last and most extreme in a series of actions taken to bring about a particular result

He gave her an ultimatum - she could either stop seeing Peter and come back to him or it was divorce. 他向她下了最后通牒——她要么不再见彼得，回到他身边，要么离婚。

On Wednesday night the UN issued its toughest ultimatum to date, demanding that all troops withdraw from the city. 星期三晚上，联合国发出了迄今为止最强硬的最后通牒，要求所有部队从该城撤出。