fellow traveler (US) or Brit fellow traveller noun
plural ∼ -ers [count] 1 : someone who is traveling in the same group or on the same train, airplane, etc., as you
▪ I struck up a conversation with one of my fellow travelers. 2 : someone who shares the opinions and beliefs of the people in a group or organization (especially the Communist Party) but does not belong to that group or organization
▪ He was not a member of the Communist Party or even a fellow traveler.
▪ I struck up a conversation with one of my fellow travelers.
▪ He was not a member of the Communist Party or even a fellow traveler.
