mat ‧ tress /ˈmætrəs, ˈmætrɪs/ BrE AmE noun [countable]
[ Date: 1200-1300 ; Language: Old French ; Origin: materas , from Arabic matrah 'place where something is thrown' ]
the soft part of a bed that you lie on
firm/soft/hard etc mattress
an old, lumpy mattress