n.拱頂石；基礎(chǔ)；重點(diǎn)

The arch is furnished with a keystone. 這個(gè)拱頂是用拱頂石裝飾的。

The keystone to any marriage is one word: "WE". 任何婚姻的基石只有兩個(gè)字:“我們”。

The second part is the keystone of this article. 這是論文的重點(diǎn)論述部分。

The essentiality of fund and financing is the keystone of expatiation. 資金和資金籌集的重要性是闡釋的重點(diǎn)。