the.com/streambed

means The channel of ground, usually sunk below the surrounding land, along which a stream flows or has flowed.

from A straightforward compound: 'stream,' from Old English 'strēam' (flowing water, related to Greek 'rhein,' to flow), plus 'bed,' from Old English 'bedd,' which carried the sense of a prepared resting place or hollow ground long before it meant furniture. The bed-for-ground sense shows up in phrases like 'seabed' and 'flowerbed' — any sunken base that holds or carries something. 'Streambed' simply puts water in that hollow.