Use the word "crumble" when something is in bad condition, when it falls apart, or when something is about to fall down.
The first sentence uses "crumble" as a verb. The second sentence uses "crumble" as an adjective. Here are some more examples:
You can also use "crumble" when describing relationships:
This old building is crumbling.
Click here to go to the Word of the Day page.
(This page was originally published on November 8. 2011.)