precedent
/ˈpresɪdənt; `prɛsədənt/ n
(a) [C] earlier decision, case, event, etc that is regarded as an example or rule for what comes later 可援为先例的判决、 事例、 事件等
create/establish/set a precedent (for sth) （为某事物）开创先例
serve as a precedent for sth 为某事物提供范例
There is no precedent for such an action. 这种行动没有先例可循.
(b) [U] existing precedents (used esp in the expressions shown) 先例（尤用於下列示例）
without precedent 没有先例
break with precedent, ie not act according to precedents 打破先例（不按先例行事）.