A waterbed, also known as a water mattress, is a bed filled with water. However, there are many synonyms for this unique type of bed that can help vary your vocabulary. Some common synonyms for the waterbed include gel mattress, fluid-filled bed, hydrosleep, waveless mattress, and aqua bed. These synonyms evoke the same essence as the waterbed, but with different wording. Additionally, some creative ways to describe a waterbed include saying that it's a bed that's filled with liquid, a mattress that mimics the feeling of floating on water, or a sleeping surface that molds to the body like a water cushion. Ultimately, no matter what you call it, a waterbed is a unique bed that can provide quality sleep, relaxation and relief.