fellow traveller 
noun
1A person who travels with another: the flight attendant asked my fellow travellers to turn off their phones...
- The ceremony will honour the men and women who tended the injured and also the walking wounded who refused to leave the scene and helped their fellow travellers.
- When travelling by train do not agree to look after the luggage of a fellow traveller or allow it to be stored in your compartment.
- If any one planning is the same trip on the same dates, i shall be more than happy to get a fellow traveller.
1.1A 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: he was certainly a fellow traveller—in the political context of the Thirties this was unremarkable...
- Sartre has been dismissed politically as a Stalinist fellow traveller.
- George Orwell once remarked to a Communist fellow traveler with whom he was having a dispute: ‘You must be an intellectual.’
- If he was a communist or even a fellow-traveller then clearly that would be a different matter but he was a committed anti-Soviet.
Derivatives
fellow-travelling
- Only they - plus a few fellow-travelling experts drawn from academia - truly comprehend the convoluted mysteries of contemporary art.
- He moved in fellow-travelling circles, modestly supporting Soviet causes.
- And then he looks at his father and shows you how he was at one point a fellow-traveling member of the Communist Party, and how he ended up becoming very right-wing, a rabid Tory, frankly.