knock the bottom out of

knock the bottom out of something

  (informal)
to harm something and make it weaker, especially by taking away the thing it needs in order to continue or be successful Ben losing his job has knocked the bottom out of our plans to buy a house.
See also: bottom, knock, of, out

knock the bottom out of

Also, knock the props out from under. Render invalid, undermine. For example, The discovery of another planet that might support life knocks the bottom out of many theories , or Jane's skilled debating knocked the props out from under her opponent. The first expression dates from the late 1800s, the variant from the first half of the 1900s.
See also: bottom, knock, of, out
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