noun

1. mud, mire, or ooze covering the ground or forming a deposit at the bottom of bodies of water
2. spongy lumps of drift ice
3. any heavy, slimy deposit, sediment, or mass, as the waste resulting from oil refining, the mud brought up by a mining drill, the precipitate in a sewage tank, the sediment in a steam boiler or crankcase, etc.

Etymology: var. of slutch, sludge, mud: akin to ME sluchched, muddy, prob. ult. < IE base *(s)leu-, to hang limply > sleet, MHG slote, mud, ooze