A mate, companion, or associate.
A companion in battle; fellow soldier.
A fellow socialist, communist or other similarly politically aligned person.
A non-hierarchical title, functionally similar to "Mr.", "Mrs.", "Miss", "Ms." etc, in a communist or socialist state.
To associate with in a friendly way.
A person who has special knowledge about the inner workings of a group, organization, or institution.
A person who is within an enclosed space.