linchpin
n
1 pin passed through the end of an axle to keep the wheel in position 輪轄; 制輪楔.
2 (fig 比喻) person or thing that is vital to an organization, plan, etc (組織、 計畫等中)關鍵性的人或事物
Controlling wages is the linchpin of the Government'spolicies. 控制工資是政府政策的關鍵.