collaborator in WordNet English dictionary

1. someone who collaborates with an enemy occupying force
   collaborator  collaborationist  quisling 
   
2. an associate in an activity or endeavor or sphere of common interest
   "the musician and the librettist were collaborators"; "sexual partners"
   collaborator  cooperator  partner  pardner 
   
3. someone who assists in a plot
   confederate  collaborator  henchman  partner in crime