MATTRESS' (4 letters) The term COMPACT BED is composed of two words, COT and MATTRESS. A COT is a small, portable bed that is often used for camping or in military barracks. It is usually made of metal or canvas and is collapsible for easy storage. A MATTRESS is a large, flat pad that is used to support the body while sleeping. It is usually made of foam, cotton, or other materials and is placed on top of a bed frame. Together, a COT and MATTRESS make up a compact bed, which is ideal for small spaces or for those who need a temporary sleeping solution.