The word mattress is usually traced back to the Arabic matrah. It comes from a root meaning to throw or cast down, so matrah referred to a place where something was thrown down or laid down.
In a bedding sense, this became associated with a mat, cushion or place for reclining.
Key points:
Mattress comes from Arabic
The root meaning is linked to throwing or laying something down
The original sense was a place where something was placed or spread