Definition of ultimatum noun from the Oxford Advanced Learner's Dictionary

 

ultimatum

 noun
noun
BrE BrE//ˌʌltɪˈmeɪtəm//
 
; NAmE NAmE//ˌʌltɪˈmeɪtəm//
 
(pl. ultimatums, ultimata
BrE BrE//ˌʌltɪˈmeɪtə//
 
; NAmE NAmE//ˌʌltɪˈmeɪtə//
 
)
 
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a final warning to a person or country that if they do not do what you ask, you will use force or take action against them to issue an ultimatum The government denied that it had presented the union with an ultimatum. Word Origin mid 18th cent.: from Latin, neuter past participle of ultimare ‘come to an end’.
See the Oxford Advanced American Dictionary entry: ultimatum