noun
Formal, somewhat literary term for disloyalty, especially toward a lord, ruler, or country. Often used in historical or political contexts.
家臣の不臣が露見し、主君は激怒した。
The retainer's disloyalty was exposed, and the lord flew into a rage.
不臣の罪で処刑された武将もいた。
Some warlords were executed for the crime of disloyalty.