退化
たいか · taika · JLPT N1 · noun
degeneration
退 — walk radical 辶 + 艮 (stop/halt)
退 combines the walking/movement radical 辶 with 艮, which carries a sense of stopping or turning back. Together they depict the action of moving backward or withdrawing. The original sense of retreating or stepping back has remained stable through history.
化 — person 亻 + spoon/upside-down person 匕
化 is an associative compound showing a standing person 亻 next to 匕, originally a depiction of a person turned upside-down. Together they suggest a figure transforming from one state to another, giving the core meaning 'change' or 'transform'. The character later extended to senses like 'convert', 'influence', and the noun suffix '-ization'.