Definition from Wiktionary, the free dictionary
- Inflexible, liable to break or snap easily under stress or pressure.
- Cast iron is much more brittle than forged iron.
- A diamond is hard but brittle.
- Not physically tough or tenacious; apt to break or crumble when bending.
- Shortbread is my favorite cold pastry, yet being so brittle it crumbles easily, and a lot goes to waste.
- (archaeology) Said of rocks and minerals with a conchoidal fracture; capable of being knapped or flaked.
- Emotionally fragile, easily offended.
- What a brittle personality! A little misunderstanding and he's an emotional wreck.
- (informal, proscribed) Diabetes that is characterized by dramatic swings in blood sugar level.
Related terms 
able to break or snap easily under stress or pressure
apt to break or crumble when bending
emotionally fragile, easily offended
- (uncountable) A confection of caramelized sugar and nuts.
- As a child, my favorite candy was peanut brittle.
- (uncountable) Anything resembling this confection, such as flapjack, a cereal bar, etc.
confection of caramelized sugar and nuts