treacherous courtier; evil adviser to a ruler
Historical/classical term for a person who gains the trust of a lord or emperor while secretly plotting against him. Often used in discussions of Chinese or Japanese court intrigue.
The history book records that troops were raised to remove the treacherous courtiers.
A classical Chinese-derived compound: 君側 (ruler's side) + の + 奸 (treachery/evil person). The exact historical origin is uncertain, but it appears in classical Chinese and Japanese texts describing court politics.