indefinable

adj.难以说明的；不确定的

There's an indefinable air of tension in this town. 这城镇里有种难以描述的紧张气氛。

The vision leaves an indefinable longing and regret. 这种景象留给人们一种莫名的渴望和遗憾。

And she had something extra, something indefinable. 她还有一些别的事，一些不能确定的事。

The Cold War came to an end unexpectedly, and America's opponents became so indefinable that it was difficult to define its national interests. 摘要冷战的结束不期而至，美国的对手变得难以确定，其国家利益也难以界定。