n.拱顶石；基础；重点
The arch is furnished with a keystone. 这个拱顶是用拱顶石装饰的。
The keystone to any marriage is one word: "WE". 任何婚姻的基石只有两个字:“我们”。
The second part is the keystone of this article. 这是论文的重点论述部分。
The essentiality of fund and financing is the keystone of expatiation. 资金和资金筹集的重要性是阐释的重点。
