愤怒 (fèn nù) is a strong, formal adjective meaning 'furious, indignant' — used in writing or serious speech for intense anger. It is stronger and more literary than 生气 (shēng qì, the everyday verb 'get angry') and 恼火 (nǎo huǒ, 'annoyed/vexed'). 气愤 (qì fèn) is similar but emphasizes righteous indignation; 不平 (bù píng) focuses on a sense of unfairness.