crumble (v.) Look up crumble at Dictionary.com
late 15c., kremelen, from Old English *crymelan, presumed frequentative of gecrymman "to break into crumbs," from cruma (see crumb). The -b- is 16c., probably on analogy of French-derived words like humble, where it belongs, or by influence of crumb. Related: Crumbled; crumbling.