An airhead is someone whose head is full of air. He or she hasn’t got any sensible or realistic ideas and is rather a silly and unintelligent person.

Airhead指脑中除了空气，空无一物的人，即我们所说的“空脑壳”或“没脑子的人”。他们的脑子想不出任何有现实意义的主意，基本上属于愚钝、缺少智慧的人。

For example:

Michael forgot to bring his passport for his flight to Sydney. What an airhead!

迈克尔去赶飞往悉尼的飞机，但忘记带护照了。真是没脑子！

The opposite of an airhead is an egghead. An egghead is a very studious and intellectual person. However it isn’t always used in a complimentary¹ manner.

Airhead的反义词是egghead，指学识渊博的人，但有时在句子里不一定表示褒奖。

For example:

John is such an egghead, he should get out more and enjoy himself.

约翰都快成书呆子了，他应该多出去转转，放松一下。