fellow-traveller
/ˈfeləʊˈtrævələ(r)/noun
1- a person who travels with another旅伴。
1.1
- a person who is not a member of a particular group or political party (especially the Communist Party), but who sympathizes with the group's aims and policies（团体或党派, 尤指共产党的）同情者, 同路人。
派生词