The Collaborative International Dictionary of English v.0.48:
collaborationist \collaborationist\ n. someone who collaborates with an enemy occupying force. Syn: collaborator, quisling. [WordNet 1.5]WordNet (r) 3.0 (2006):
collaborationist n 1: someone who collaborates with an enemy occupying force [syn: collaborator, collaborationist, quisling]