万恶 means 'extremely evil' and is often used as a strong attributive adjective in political or moral condemnation, especially in the fixed phrase 万恶的旧社会 (the evil old society) referring to pre-1949 China. It also appears in 万恶之源 (the root of all evil), where it functions as a noun meaning 'all evils'. The word carries heavy ideological weight and is not used lightly in everyday conversation.