Collaborationist (noun)

A person who collaborates with an enemy occupying force, especially during a time of war.

Origin:

From collaboration + -ist.

Examples:

1. The collaborationist was accused of providing information to the enemy and was tried for treason.
2. Many people in the occupied country saw the collaborationists as traitors and despised them.
3. The collaborationist was shunned by the local community after the war and lived the rest of his life in disgrace.
4. The historian's research focused on the role of collaborationists during the Nazi occupation of France.
5. The collaborationist's testimony provided valuable insight into the inner workings of the enemy's operations.