sludge

American  

[sluhj] / slʌdʒ /

noun

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

• de-sludge verb (used with object)

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

Example Sentences

While the tariff sludge remains, markets digested mixed economic data.

From Barron's • Feb. 20, 2026

The Times built its own internal search engine to sort through the sludge.

From Slate • Feb. 4, 2026

Tougher controls over the spreading of sewage and septic tank sludge to land as fertiliser in farming are also proposed, as are limits on using digestate from anaerobic digestion plants.

From BBC • Feb. 3, 2026

The book, co-authored by the brand’s founder, is a pointed history of commercial pet food that leaves the reader uneasy that their dog might be consuming toxic sludge.

From The Wall Street Journal • Jan. 28, 2026

Up the wet, winding boardwalks and through stretches of mud that cake my hiking boots in sludge.

From "The Sea in Winter" by Christine Day

Related Words

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