turncoat (n.)

• apostate
• backslider
• betrayer
• cockatrice
• collaborationist
• collaborator
• conspirator
• convert
• defector
• deserter
• double-crosser
• double-crossing
• double-dealer
• informer
• intriguer
• machinator
• mugwump
• plotter
• proselyte
• quisling
• rat
• recidivist
• recreant
• renegade
• reversionist
• schemer
• secessionist
• separatist
• serpent
• snake
• spy
• straggler
• strikebreaker
• tergiversator
• timeserver
• traitor
• treasonist
• trimmer
• turnabout