/ˌʌndəˈlaɪ ||; ˌʌndɚˈlaɪ/verb [T] (present participle underlying;past tense underlay /-ˈleɪ ||; -ˈle/ past participle underlain /-ˈleɪn ||; -ˈlen/) (formal 正式) to be the basis or cause of sth 为…的基础或原因: It is a principle that underlies all the party's policies. 该党的所有政策都以此原则为基础。