double 用作形容词时后接单数名词

an egg with a double yolk  双黄蛋

He did it with a double purpose. 他这样做有双重目的。

We must make a double check of this safety apparatus.

我们须对这一安全设备作两次仔细的检查。

He is playing double dealing.

他在耍两面派。

[注意：double meaning 前无a，如换用a double game，前须有a，意思相同]

Because he has published a few articles, he considers himself a real doubledome.

他因为发表了几篇文章，就自以为是很有学问的人了。

[dome 原指“圆房顶”，后引申为人的头脑，doubledome 指“有双重头脑”。]

It has the double advantage of being cheap and at the same time very good.

它具有价廉物又美的双重优点。