The word 封闭 is formed by combining two characters, 封 and 闭, which each contribute a related meaning to create a single, reinforced concept. 封 carries the core idea of sealing something, like with a stamp or a boundary, while 闭 means to shut, close, or obstruct. When placed together, they operate not as separate actions but as a fused, logical pair: to first seal or cover (封) and then to shut or close off completely (闭), resulting in the comprehensive meaning of "to close up", "to seal off", or "to enclose", picturing a state of total isolation or impermeability.