A quisling is a person who helps an enemy that has taken control of their own country — not just any bad person, and not a spy from outside, but someone from inside who works with the occupiers. It is a hard, bitter word, born in the Second World War. People use it in history, news, and political argument when they want to say “traitor who sided with the invaders.” You will not hear it much in everyday chat about small things; it is too heavy for that. Newspapers sometimes still capitalise it, because it began as a man’s name, but as a common noun it is usually written with a small q. There is a rare verb, to quisling, meaning to act in that way, but almost everyone meets only the noun. Though actually, people do stretch it: they may fling it at any politician they think is selling the country out, even when no foreign army is in the streets. That stretch is angry rhetoric, not the original, tighter sense.

通敵者、賣國賊。意思上有點像過去說的「漢奸」，但 quisling 來自一個挪威人的名字，不是中文自己長出來的詞。