crumb (n): a very small piece of food, especially of bread or cake, that has fallen off a larger piece
She stood up and brushed the crumbs from her sweater.
ok, now I want to change the definition a little bit. That is:
a very small piece of glass that has fallen off a larger piece
do we say "glass crumb" as just as we often say "food crumb"? If not, what is the word to say?
also other kinds of materials? "wood crumb" or "stone crumb"?
As others have said, the general word for a broken piece of glass is "shard".
You could also say "fragment", "chip", or "broken piece of glass". Those words could apply to almost anything solid. "A fragment of glass", "a fragment of wood", "a fragment of bone", "a fragment of copper", etc. (You wouldn't use these words for liquids.)
Small pieces of wood, like no more that a few square inches, are often called "wood chips". If you're talking about a bigger piece, like a fallen tree branch, it's generally called simply "a piece of wood". Maybe carpenters of a specific word for it, but I don't know of one. Oh, and very small pieces of wood, like fraction of an inch, are called "sawdust".
No, we don't. Pieces of broken glass are often called shards https://www.vocabulary.com/dictionary/shard
We would only use crumb when speaking of a non-food substance if it was something with a soft texture similar to bread, such as rotten wood. For stone or (hard) wood it would be chips or fragments.
When glass, porcelaine or stone breaks, it usually shatters. What you get are shards (larger pieces) and splinters (small, often longish pieces).
If you talk about crumbles, I imagine very small pieces, typically created not by just dropping the glass, but for example by stepping on the glass or otherwise applying extra force, creating finer particles than simply dropping it would cause. Even finer would be dust, very, very fine particles.
