鍛

A phono-semantic compound consisting of:

金 (metal) — semantic component, indicating relation to metalworking;

段 (duàn) — phonetic component, providing the sound. The structure conveys working metal through repeated processing, especially heating and shaping.
Semantic development: - heating metal; - hammering and shaping; - strengthening through repeated processing; - training body or mind. Thus, 鍛 evolved from physical forging to personal cultivation and discipline.

단련 (鍛鍊 / 鍛練) — training; discipline

제련 (製鍛) — forging; metalworking

The concept of 鍛 is central to traditional craftsmanship, especially in blacksmithing and weapon-making. In modern usage, it is strongly associated with self-improvement and discipline (e.g., physical training).

Compared to 練, which implies repeated practice, 鍛 carries a sense of intensity and transformation. The metaphor reflects an important idea: true strength is forged through hardship and repetition.
Related characters: 鍊 — to refine (especially by heating)

冶 — to smelt; metallurgy

鍛 — forging

練 — to practice; to train

Among these, 鍛 emphasizes forceful shaping and strengthening, often through effort.