"surely we would all agree that if anyone deserved the death penalty, then these filthy quislings did?"
Seated, left to right: Quisling, Himmler, Terboven, von Falkenhorst
Creative Commons Attribution Share AlikeSeated, left to right: Quisling, Himmler, Terboven, von Falkenhorst - Credit: Bundesarchiv, Bild 101III-Moebius-029-12 / Möbius / CC-BY-SA

The term "quisling" is similar to calling someone a "Benedict Arnold"; it means "traitor," and derives from Vidkun Quisling, a Norwegian politician who betrayed his country by cooperating with the Nazis when they took over Norway in 1940. He was executed by firing squad in 1945.

According to the Online Etymology Dictionary, "quisling" was first used as a synonym for "traitor" in the London Times on 15 April 1940. Lewis's use of the word, then, is relatively modern, since he was writing in 1942.