Treason
From the Simple English Wikipedia, the free encyclopedia that anyone can change
Treason is when a person acts against his country. For example, somebody might help another country fight a war against his country by telling secrets. Treason is a common word, but different countries have different laws and punishments against it.
The word for a person who is treasonous is “traitor”. Some famous traitors are Judas, Benedict Arnold, Pétain and Quisling.