a person who betrays another, a cause, or any trust.

a person who commits treason by betraying his or her country.

noun

loyalist

noun

apostate , backslider , back-stabber , benedict arnold * , betrayer , conspirator , deceiver , defector , deserter , double-crosser , fink * , hypocrite , impostor , informer , intriguer , judas * , miscreant , quisling , rebel , renegade , snake * , sneak * , snitch * , snitcher , spy , squealer * , stool pigeon * , tattletale , traducer , treasonist , turncoat , two-timer , whistle-blower , wolf * , judas , agent provocateur , benedict arnold , collaborator , mole , plant , recreant , sleeper , stoolie , stool pigeon , subversive , tergiversator