What is the noun of crumbling?

The Word 'crumbling' is a noun form, a gerund, the present participle of the verb to crumble that functions as a noun.

The present participle of the verb also functions as an adjective.

The Word 'crumble' is both a verb and a noun.

The noun 'crumble' is a Word for a flour mixture topping for fruit pastry and cakes.

Examples:

This old house is crumbling around us. (verb)

There is a lot of crumbling at the base of the concrete. (noun)

The castle was surrounded by a crumbling wall. (adjective)

If you crumble cheese over that, it will be delicious. (verb)

This is mother's recipe for cherry crumble. (noun)