quisling
From Longman Dictionary of Contemporary Englishquislingquis‧ling /ˈkwɪzlɪŋ/ noun [countable] old-fashioned PGCPMsomeone who helps an enemy country that has taken control of their own countryOrigin quisling (1900-2000) Vidkun Quisling (1887-1945), Norwegian politician who helped the Nazis in Norway during World War II