unprecedented
/ʌnˈpresɪdentɪd; ʌn`prɛsəˌdɛntɪd/ adj
without precedent; never having happened, been done or been known before 无前例的; 前所未有的; 空前的
unprecedented levels of unemployment 失业率达到的前所未有的严重程度
a situation unprecedented in the history of the school 该校自有校史以来未曾出现过的情况.