linchpin
/ˈlɪntʃpɪn/(亦作 lynchpin)
noun
1
- a pin passed through the end of an axle to keep a wheel in position制轮楔。
2
- a person or thing vital to an enterprise or organization（企业、组织中的）至关重要的人物; 关键因素：
regular brushing is the linchpin of all good dental hygiene.
经常刷牙是保持牙齿卫生的关键。
词源
late Middle English: from Old English lynis （in the sense 'linchpin'） + -PIN.