Box spring and Mattress

Box spring noun - A coiled bedspring in a frame that is covered with cloth.

Mattress and box spring are semantically related In some cases you can use "Mattress" instead a noun phrase "Box spring".

Mattress noun - A large thick pad filled with resilient material and often incorporating coiled springs, used as a bed or part of a bed.

Box spring and mattress are semantically related in bedding topic. You can use "Box spring" instead a noun "Mattress".