The Collaborative International Dictionary
Water bed
Water bed \Wa"ter bed`\ A kind of mattress made of, or covered with, waterproof fabric and filled with water, thus providing uniform support to the body lying on it; -- also a bed constructed so as to contain such a mattress. It is used in hospitals for bedridden patients, as well as in some private homes.
Wiktionary
water bed
n. (alternative spelling of waterbed English)
WordNet
water bed
n. a bed with a mattress made of strong plastic that is filled with water