'crumbly' originates from the English word 'crumb,' which comes from the Old English 'cruma,' meaning 'fragment or small piece.'

'cruma' evolved into the Middle English word 'crumbe,' and eventually became the modern English word 'crumb.' The adjective form 'crumbly' was derived from 'crumb.'

Initially, it referred to something that could be broken into crumbs, and this meaning has largely remained the same in modern usage.