The word 肮脏 is formed by combining two characters, 肮 and 脏, which both individually relate to concepts of filth and impurity. 肮 originally referred to the grime or dregs on the neck of an animal or person, a very physical, surface-level dirt, while 脏 (臟/髒) relates to internal organs or moral corruption, suggesting a deeper, inherent foulness. Their pairing creates a powerful, layered concept of dirtiness that is both outwardly visible and inwardly rotten, reinforcing and intensifying the single idea of being utterly unclean through this synergistic, dual-character structure.