linchpin
n
1 pin passed through the end of an axle to keep the wheel in position 轮辖; 制轮楔.
2 (fig 比喻) person or thing that is vital to an organization, plan, etc (组织、 计画等中)关键性的人或事物
Controlling wages is the linchpin of the Government´spolicies. 控制工资是政府政策的关键.