A monks bench is a piece of furniture where a tabletop is set onto a chest in such a way that when the table was not in use, the top pivots to a vertical position and becomes the back of a Settle

Settle (furniture)

A settle is a wooden bench, usually with arms and a high back, long enough to accommodate three or four sitters.They are commonly movable, but occasionally fixed. It shares with the chest and the chair the distinction of great antiquity...

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This was a very useful form at a time when many homes had a large room used for multiple functions, because it allowed a large dining table to swing up and out of the way.