The word 挡住 is formed by combining the character 挡, which carries the core meaning "to block" or "obstruct", with the character 住, which here adds the crucial sense of "fixing that action in place" or "achieving a result of staying". It’s a conceptual fusion where the first element provides the primary action (blocking), and the second element acts as a complement that denotes the successful completion or sustained effect of that action, effectively visualizing something being blocked and then held in that stopped state.