A quisling is a traitor, more specifically a traitor who collaborates with the enemy to promote occupation and suppression of a native people. This word is of Norwegian origin, making it one of the few Norwegian terms to enter the English language, and the history of “quisling” is actually quite fascinating. Needless to say, the Norwegians are not particularly proud of this particular word of Norwegian origin, and they would prefer to see people remembering linguistic contributions like “ski,” “fjord,” and “slalom.”
This slang term emerged during the Second World War, when a Norwegian politician by the name of Vidkun Quisling advocated for a German occupation of Norway, and actively worked to hasten a German occupation. On 1 February 1942, he took power in Norway as the Minister President, and set about encouraging Nazi values and promoting the German cause in Norway.
In the end, Quisling's plan backfired, and actually stimulated quite a local resistance as angry Norwegians fought the German occupation. Under Quisling, Norway expelled Jews to certain death in Nazi camps, and the country also had a Nazi party branch, and its own branch of the SS. As in other Occupied nations during the war, resistance to the government had to be carried out with stealth, as it could be deadly for people who were caught. Loyal Norwegians viewed Quisling as the ultimate traitor after he sold Norway out to the Germans in exchange for ultimate power.
Quisling himself was captured and executed after the war, in one of the last executions permitted in Norway. Even during the war, political cartoons started using “quisling” as a shorthand for a traitor, as in jokes like “'I am Hitler, who are you?' 'I am Quisling!' 'Yes, but what is your name?'” By the end of the war, the slang term had spread to other parts of Europe, and it had entered the English lexicon, appearing notably in a wide range of potboiler novels and film noirs published after the war.
Collaboration can be an especially insidious form of treachery, so it is perhaps not surprising that “quisling” became a slang term, since Quisling was one of the most outspoken and notable collaborators of the Second World War. Over time, the term came to refer to any form of treachery, not necessary collaboration on a governmental scale. As a general rule, being called a quisling is an insult, as it implies that people view someone as not just a traitor, but an active collaborator with an enemy.