Longman Dictionary of Contemporary English - crumble

~1 v 1 also crumble away to break apart into little pieces, or make something do this  (Billy crumbled the bread in his fingers.) 2 if a building crumbles, it is old and starting to fall down  (Britain's crumbling schools) 3 also crumble away if your determination, courage etc crumbles, it becomes weak or fails  (Brigg's resolve crumbled and he reached for the whisky bottle.) 4 if a military operation, government etc crumbles, it loses its power and its effectiveness  (a crumbling empire) ~2 n a cooked dish of fruit covered with a dry mixture of flour, butter, and sugar  (apple crumble)