go-between
noun [ C ] uk/ˈɡəʊ.bɪˌtwiːn/ us/ˈɡoʊ.bɪˌtwiːn/
中间人，掮客
someone who takes messages between people who are unable or unwilling to meet
The ambassador has offered to act as a go-between for the two countries involved in the conflict. 大使主动提出愿在发生冲突的两国间担当中间人。
Synonym: intermediary