fifth wheel
US /ˌfɪfθ ˈwiːl/
UK /ˌfɪfθ ˈwiːl/

1.
多余的人, 累赘
a person who is in a situation where they are not needed or are superfluous
:
•
I felt like a fifth wheel on their romantic dinner.
在他们的浪漫晚餐上,我感觉自己像个多余的人。
•
When they started talking about their inside jokes, I knew I was the fifth wheel.
当他们开始谈论他们的内部笑话时,我知道我是个多余的人。