/ˌʌltɪˈmeɪtəm ||; ˌʌltəˈmetəm/noun [C] (plural ultimatums) a final warning to sb that, if he/she does not do what you ask, you will use force or take action against him/her 最后通牒: I gave him an ultimatum -- either he paid his rent or he was out. 我向他下了最后通牒，他要么付房租，要么离开。