sludge
n. uncountablen. thick, wet, and sticky mud or waste. It is usually the dirty material left over from industrial processes or cleaning.
n. thick, soft, wet mud or a similar viscous mixture of liquid and solid components, often as a byproduct of industrial or sewage treatment.
The workers had to clear the thick sludge from the pipes.
After the heavy rains, a layer of dark sludge covered the bottom of the garden path.
Environmental inspectors discovered that the factory had been illegally dumping toxic sludge into the local river system for several months.
From Middle English slugge, sluche (“mud, mire”), probably an alteration of Middle English sliche, slicche ("mud, slush, tar"; whence Modern English slitch), from Old English sliċ, from Proto-West Germanic sliki, slīk, from Proto-Germanic slikiz, *slīką (“mud, slush”). Cognate with Dutch slijk, German Schlick. Compare also slush.