What is a flat piece of stale bread used as plate called in medeavil times?

There's no specific name for a flat piece of stale bread used as a plate in medieval times, but it was a common practice! Here's why:

* "Trenchers" were the most common way to eat in medieval times. These were made from a thick, often stale, piece of bread which acted as a "plate" to catch food scraps.

* "Treenware" (wooden plates, bowls, and spoons) were used by those with more means, but trenchers were the norm for most people.

* "Crusts" or "pieces of bread" were likely what people used as plates in the absence of a trencher.

The use of bread as a plate wasn't just practical, it also served as a way to utilize leftover bread and ensure nothing was wasted.

There isn't a single word to describe this, but you can certainly say:

* "A piece of stale bread used as a plate"

* "A trencher"

* "A crust"

* "A bread plate" (though this term is more modern)

Keep in mind that the language of medieval times was different, so there might have been less formal terms used at the time.