weak sister

American  

noun

Informal.

1. a vacillating person; coward.

2. a part or element that undermines the whole of something; a weak link.

---

weak sister British  

noun

1. informal  a person in a group who is regarded as weak or unreliable

---

Etymology

Origin of weak sister

First recorded in 1855–60

Example Sentences

To people in Sandy Hook, "Trump comes across as a leader. This fellow, Biden, he comes across as a weak sister," Mr Kinner said.

From BBC

This is Ethan, who, I’m afraid, turns out to be something of a weak sister, going all shaky on the second date after Nikki smashes in the teeth and breaks the arm of a would-be mugger.

From Washington Post

You don't want a weak sister in there, nor do you want for one course to offer amenities or an experience that shouts down the other two.

From Golf Digest

One theory goes that by talking tough, Trump is alerting the world that the United States is no longer the weak sister, if I may use an old expression, it had become under President Barack Obama.

From Washington Post

Fear is a very weak sister and, yes, they really should get rid of those brooding teenagers and maybe Travis too.

From New York Times