either-or
adjective [ before noun ] uk/ˌaɪ.ðərˈɔːr/ /ˌiː.ðərˈɔːr/ us/ˌiː.ðɚˈɔːr/ /ˌaɪ.ðɚˈɔːr/
必须（或只能）两者择一的;非此即彼的
used to refer to a situation in which there is a choice between two different plans of action, but both together are not possible
It's an either-or situation - we can buy a new car this year or we can go on holiday, but we can't do both. 这就叫鱼和熊掌不可兼得——今年我们要么买辆新车，要么去度假，但只能做一样。