Something that's brittle breaks easily when you press or hit it.
The word "brittle" is often used to describe food like crackers or cookies that crack when you bite into them. You might hear someone say, "These chocolate chip cookies are too brittle - they break apart as soon as I try to eat them." It can also be used for objects made of materials that are prone to breaking under pressure, like a thin piece of metal or ice.
How common is "brittle"?
Word brittle is considered rare in modern English. It has a balanced usage among all categories: speech, fiction, newspapers and academic texts.
Definitions
adjective
Inflexible; liable to break, snap, or shatter easily under stress, pressure, or impact; crackly.
Example: Cast iron is much more brittle than forged iron.
Not physically tough or tenacious; apt to break or crumble when bending.
Example: Shortbread is my favorite cold pastry, yet being so brittle it crumbles easily, and a lot goes to waste.
(archaeology, of rocks, minerals, etc) Tending to fracture in a conchoidal way; capable of being knapped or flaked.
Emotionally fragile, easily offended.
Example: What a brittle personality! A little misunderstanding and he's an emotional wreck.
(engineering, computing, of a system) Poorly error- or fault-tolerant; having little in the way of redundancy or defense in depth; susceptible to catastrophic failure in the event of a relatively-minor malfunction or deviance.
(informal, proscribed, of diabetes) Characterized by dramatic swings in blood sugar level.