朽

A phono-semantic compound consisting of:

木 (wood) — semantic component, indicating something organic (especially trees); 丂 (kǎo) — phonetic component, providing the sound. The structure conveys wood undergoing decay, forming the basis of meanings like “to rot” or “to deteriorate.”
Semantic development: - wood decaying; - rotting or decomposition; - deterioration over time; - moral or institutional decay (metaphorical). Thus, 朽 expanded from physical decay to abstract decline.

In Korean, 朽 appears mainly in formal, literary, or abstract expressions.

부후 (腐朽) — decay; corruption

노후 (老朽) — aging; deterioration (of buildings, systems, etc.)

불후 (不朽) — immortality; imperishable

The expression 朽木不可雕也 (rotten wood cannot be carved) is a well-known classical saying, meaning someone beyond improvement. In contrast, 不朽 (not decaying) conveys the idea of lasting forever, especially in literature or achievements. The character carries both physical and moral implications, making it common in philosophical and literary texts. Its imagery of decaying wood provides a vivid metaphor for inevitable decline if not maintained.
Related characters: 腐 — rot; corruption

壞 — ruin; collapse

衰 — decline; weaken

敗 — defeat; ruin

Among these, 朽 emphasizes gradual, natural decay, often over time.