sludge

American  

[sluhj] / slʌdʒ /

noun

• sludges
  plural

1. mud, mire, or ooze; slush.

2. a deposit of ooze at the bottom of a body of water.

3. any of various more or less mudlike deposits or mixtures.

4. the sediment in a steam boiler or water tank.

5. broken ice, as on the sea.

6. a mixture of some finely powdered substance and water.

7. sediment deposited during the treatment of sewage.

8. Also called activated sludge.  Bacteriology. sewage sediment that contains a heavy growth of microorganisms, resulting from vigorous aeration.

9. a fine, mudlike powder produced by a mining drill.

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sludge British  

/ slʌdʒ /

noun

1. soft mud, snow, etc

2. any deposit or sediment

3. a surface layer of ice that has a slushy appearance

4. (in sewage disposal) the solid constituents of sewage that precipitate during treatment and are removed for subsequent purification

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Other Word Forms

Derived Forms

• de-sludge
  verb (used with object)

Inflected Forms

Nouns

• sludges
  plural

Etymology

Origin of sludge

First recorded in 1640–50; variant of dialectal slutch, slitch, Middle English slich “slime, wet mud” (compare its derivative slucched “muddy”); apparently of expressive origin

Explanation

Sludge is thick, damp, almost sticky stuff. If your friend dares you to climb through an old sewer pipe, you might want to check first to see if it's full of sludge. Sludge is often used to talk about the byproduct of a process like sewage treatment or oil refining, but you can use it for any viscous goop. Sludge floating in your fish tank is a sign that you should clean the water, and sludge inside a car's engine can affect the way the car runs. Sludge is a bit of a mystery — it may come from the Middle English slutch, "mud," or might be related to slush.

Example Sentences

See Examples For:

sludge sludges

But if those particles are collected inside a flask, they form a dense suspension of burned tobacco -- a tar-like sludge.

From Science Daily ● Sep. 13, 2026

The kind of groove your tires make driving to Big Bear in December without chains: an icy trench filled with frustration, exhaustion and everyday sludge.

From Los Angeles Times ● Sep. 11, 2026

The wave tore through the Rasuwagadhi hydropower plant where Adhikari worked, swallowing buildings and leaving only dark-gray sludge.

From The Wall Street Journal ● Sep. 9, 2026

“A half-hour of hard-driving rock led straight into mid-tempo sludge like ‘Fingerprint File,’ a pointless but not purposeless exercise whose supposed function was to prove that Jagger could play guitar competently.”

From Salon ● Sep. 8, 2026

The hydrocarbons should remain on Titan, covering the surface with a brownish tarry organic sludge, something like that produced in experiments on the origin of life on Earth.

From "Cosmos" by Carl Sagan

"When sewage sludges are spread across the fields, those toxic compounds could be released into the air," Katz said.

From Science Daily ● Apr. 11, 2026

These little guys live in basically every natural setting in the world, including deserts, soils, and, in particularly unlucky cases, the sludges of the human body.

From Slate ● Mar. 8, 2024

While working in a lab in the Netherlands in the late 2000s, Strous noticed that a type of methane-feeding bacteria often found in lake sediments and wastewater sludges had a strange way of life.

From Scientific American ● Aug. 22, 2023

The targeted radioactive waste included plutonium-contaminated filters, graphite molds, sludges containing solvents and oxidized uranium generated during nuclear weapons production work at the Rocky Flats Plant in Colorado.

From Seattle Times ● Jan. 3, 2022

With regard to the manurial value of the resulting sludges, much difference of opinion has existed.

From Manures and the principles of manuring by Charles Morton Aikman

Related Words

• goo
• grease
• gunk
• muck
• sediment
• silt
• slime