The definition of crumbly is made of crumbs, or easily broken into small parts.
An example of something crumbly is a cookie that will not stay in one piece.
- apt to crumble; easily crumbled
- crumblike; consisting of crumbs or small particles
Easily crumbled; friable.
(comparative crumblier, superlative crumbliest)
From crumble + -y.