A bed with a mattress filled with water instead of springs or foam, popular in the 1970s and 80s.
Compound of 'water' (from Old English 'wæter') and 'bed' (from Old English 'bedd'). The waterbed concept was patented in 1968, though the term combines two ancient words in a modern way.
Waterbeds were so trendy that they became a symbol of 1970s excess and groovy living—yet they're surprisingly practical for people with back pain or arthritis because water distributes weight evenly across your body, the same physics principle used in flotation tanks for therapy.
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