The word **退化 (tuìhuà)** is a compound formed through the combination of two meaningful characters: **退 (tuì)**, meaning "to retreat," "to decline," or "to move backward," and **化 (huà)**, meaning "to change," "to transform," or "-ization." Together, they create a conceptual whole where **退** provides the directional or qualitative sense of regression or decline, and **化** indicates the process of undergoing that change. Thus, **退化** literally means "to change into a backward/declined state," effectively conveying the concept of *degeneration*, *atrophy*, or *devolution*, whether in biological contexts (e.g., the loss of a function in a species) or metaphorical ones (e.g., the deterioration of a skill).