a bed having a liquid-filled rubber or plastic mattress in a rigid, often heated, waterproof frame, and providing a surface that conforms to the sleeper's body in any position.
1610s, "a bed on board a ship," from water (n.1) + bed (n.). As a water-tight mattress filled with water, it is recorded from 1844, originally for invalids. Reinvented c.1970 as a hip furnishing.
