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sludge

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.

sludge (countable and uncountable, plural sludges)

Solids separated from suspension in a liquid.
- 2013 June 29, “High and wet”, in The Economist, volume 407, number 8842, page 28:
  Floods in northern India, mostly in the small state of Uttarakhand, have wrought disaster on an enormous scale. […] Rock-filled torrents smashed vehicles and homes, burying victims under rubble and sludge.
A residual semi-solid material left from industrial, water treatment, or wastewater treatment processes.
A sediment of accumulated minerals in a steam boiler.
A mass of small pieces of ice on the surface of a water body.
(uncountable, music) Ellipsis of sludge metal.
(behavioral science) Institutional policies that introduce tedium and inefficiency in processes.
- [2025 June 29, Chris Colin, “That Dropped Call With Customer Service? It Was on Purpose.”, in The Atlantic‎, retrieved 29 June 2025, Ideas:
  In the 2008 best seller Nudge, the legal scholar Cass R. Sunstein and the economist Richard H. Thaler marshaled behavioral-science research to show how small tweaks could help us make better choices. An updated version of the book includes a section on what they called “sludge”—tortuous administrative demands, endless wait times, and excessive procedural fuss that impede us in our lives.]

generic term for separated solids — see also slop,‎ mush

residual material from a process

sediment of minerals in a steam boiler

small pieces of ice

sludge (third-person singular simple present sludges, present participle sludging, simple past and past participle sludged)