weak sister

American  

noun

Informal.

1. a vacillating person; coward.

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

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weak sister British  

noun

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

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Etymology

Origin of weak sister

First recorded in 1855–60

Example Sentences

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

There’s no weak sister in conference.

From Washington Times

The N.F.L.’s player’s union long has been a labor weak sister.

From New York Times

However, the mumps portion of the vaccine is estimated to be only about 88 percent effective – it’s the “weak sister” of the three, as Paul Offit, professor of pediatrics at Children’s Hospital of Philadelphia, told me during the NHL mumps outbreak last fall.

From Forbes

Not even the weak sister in the group, KB Home, out with weak numbers on Tuesday, derailed the best in class.

From Forbes