crumble

Concise Oxford English Dictionary © 2008 Oxford University Press:
crumble/ˈkrʌmbl/

▶verb break or fall apart into small fragments.

■ cause (something, especially food) to crumble.

■ disintegrate gradually: the party's fragile unity began to crumble.

▶noun Brit. a pudding made with fruit and a topping of flour and fat rubbed to the texture of breadcrumbs.

– origin ME: prob. from an OE word rel. to crumb.