The word 堵塞 is formed by combining the characters 堵 and 塞, each contributing related meanings of blocking or obstructing. 堵 denotes stopping up or barricading, often physically, while 塞 implies filling in or plugging a space. Together, they reinforce the idea of a clog or obstruction, resulting in a compound word that conveys thorough blockage, as in a congested passage or sealed opening.