bulwark
/ˈbulwək; `bʊlwɚk/ n
1 wall, esp of earth, built as a defence 壁垒（尤指用泥土堆砌者）; 防御工事.
2 (fig 比喻) person or thing that supports, defends or protects 支持, 防御或保护的人或事物
Democracy is a bulwark of freedom. 民主是自由的保障.
3 (usu pl 通常作复数) ship's side above the level of the deck 舷墙（甲板线以上的船侧）.