The word 堵住 is formed by combining the character 堵, which means "to block" or "to stop up", with the character 住, which here functions as a resultative complement indicating that the action achieves a firm, fixed, or successful state. Together, they create a verb meaning "to block up completely" or "to seal off", where the second character emphasizes the attainment and persistence of the blocked condition resulting from the action of the first.