fifth wheel

n. 第五个轮子, 半拖车接轮, 转向轮, 备用轮, 多余的人（或物）

例句与用法：

Beware of the fifth column. They often infiltrate into key positions and seek to undermine the body politic from within.

要提防隐蔽的敌人，他们经常渗透到关键岗位企图从内部破坏国家政体。

词形变化：

名词: fifth columnism |

详细释义：

ph.

1. 第五个轮子; 备用轮

2. 【喻】多余的人(或物)

Since my girlfriend didn't come, I was a fifth wheel at the party.

因为我女友没有来, 我在舞会上成为多余之人。

We decided to fire that worker, he was just a fifth wheel.

我们决定开除那个工人, 他不过是个多余无用之人。