Quisling
Etymology
An eponym from Vidkun Quisling, the Norwegian politician who aided the Nazi invasion of 1940 and led a collaborationist government under German occupation. The Times of London turned his name into a common noun within weeks of the invasion, and it stuck across many languages.
noun · /KWIZ-ling/
A traitor who collaborates with an occupying enemy power, especially by heading a puppet regime.
What it names
A single word for the specific treachery of the collaborator — not the foreign invader, but the local who serves them against his own people.
Example
The resistance reserved its deepest contempt not for the occupiers but for the quislings who informed on their neighbors.
Related idea
Sharper than a generic traitor and distinct from a fifth column, which is a hidden group of internal sympathizers; a quisling is typically a named, public collaborator who openly governs on the enemy’s behalf.
See also