The word 补充 is formed through the common Chinese method of ideographic synthesis, where two independent characters, each with their own meaning, are combined to create a new, compound concept. The first character, 补 (bǔ), carries the core idea of mending, repairing, or adding to something deficient. The second character, 充 (chōng), contributes the notion of filling, making full, or sufficient. When placed together, they create a sequential and reinforcing logic: one first adds to (补) something in order to fill it up or make it complete (充), thus perfectly encapsulating the meaning "to supplement" or "to replenish".