designated driver
noun [ C ] uk/ˌdez.ɪɡ.neɪ.tɪd ˈdraɪ.vər/ us/ˌdez.ɪɡ.neɪ.t̬ɪd ˈdraɪ.vɚ/
指定司机（指一群人中同意不喝酒并负责开车接送他人去往或离开聚会场所的人）
one person in a group who agrees not to drink alcohol in order to drive the other people to and from a place where they will drink alcohol
Tom said he'd be the designated driver when we go out tonight. 汤姆说今晚外出时他不喝酒，作我们的司机。