Definitions:

1. an associate in an activity or endeavor or sphere of common interest noun
   • The assist maker and the goal scorer are were collaborators.
2. someone who assists in a plot noun
   • All of the collaborator were arrested after the ring leader gave them up.
3. someone who collaborates with an enemy occupying force noun
   • The main collaborators were executed after the war.

Synonyms:

• collaborationist
• confederate
• cooperator
• pardner
• partner
• quisling