The word 拦住 is formed by combining the character 拦, which means "to block" or "to obstruct", with the character 住, which in this context adds the sense of "firmly", "securely", or "to a stop". The two characters fuse together to create a single action concept where the blocking action initiated by 拦 is completed and solidified by 住, resulting in the comprehensive meaning of "to block and hold in place" or "to successfully stop something/someone".