It comes from the Old French word "materas," which itself comes from the Latin word "matera," meaning "mother." This might seem strange, but it makes sense when you consider the original meaning of "materas" in Old French: a "mother" or "base" for something else. Think of a mother as the foundation of a family - the "materas" was essentially the foundation of a bed, providing support and comfort.
The word "materas" entered English around the 14th century, and over time it evolved into "mattress."
So, the next time you lie down on your mattress, you can think of it as the "mother" of your sleep, providing a comfortable base for rest!