The word 充当 (chōngdāng) is a compound verb formed through the combination of two semantically similar characters: 充, which carries the core meaning of "to fill," "to serve as," or "to act as," and 当, which means "to undertake," "to bear," or "to work as." Together, they create a synergistic meaning where 充 emphasizes the action of assuming or filling a role, and 当 reinforces the notion of undertaking or functioning in that capacity. This morphological structure, known as a coordinative or synonymous compound, results in a verb that means "to serve as," "to act as," or "to play the role of," often with a slight connotation of temporarily or inadequately fulfilling a position.