Collaborator (noun)

1. A person who works jointly with another or others in a project, enterprise, or task.
2. A person who cooperates, usually willingly, with an enemy, especially with an occupying force.
3. A person who aids and abets in the commission of a crime.

Origin:

Early 19th century: from latin collaborat- "worked with", from the verb collaborate.

Examples:

1. She was a collaborator on the research project.
2. He was a collaborator with the enemy during the war.
3. The traitor was a collaborator in the plot to overthrow the government.
4. The company was looking for collaborators to develop new products.
5. She was a collaborator in the design of the website.