sludge

noun

ˈsləj 

1

: mud, mire

especially : a muddy deposit (as on a riverbed) : ooze

2

: a muddy or slushy mass, deposit, or sediment: such as

a

: precipitated solid matter produced by water and sewage treatment processes

b

: muddy sediment in a steam boiler

c

: a precipitate or settling (such as a mixture of impurities and acid) from a mineral oil

3

: slush sense 5

sludgy

ˈslə-jē 

adjective

Synonyms

• mud

Examples of sludge in a Sentence

after a day of heavy rain, the fairgrounds had turned into pure sludge

I can't bring myself to read that sludge.

Recent Examples on the Web

Meanwhile, the onset of the rainy season has exacerbated already deplorable conditions, transforming dust into thick sludge, flooding fragile shelters, and bringing swarms of malaria-carrying mosquitoes. —Charlie Campbell, Time, 4 Sep. 2025

The standard provided improved protection for modern gasoline engines, including requirements for Low-Speed Pre-Ignition (LSPI), timing chain wear, and better piston deposit and sludge control. —Michael Harley, Forbes.com, 25 Aug. 2025

The wastewater exits the home into the septic tank, where solids settle to the bottom of the tank to form a sludge layer, and the lighter waste forms a scum layer that floats at the top. —Timothy Dale, Better Homes & Gardens, 14 Aug. 2025

The problems range from sludge build up and even cracked engine blocks. —John Paul Senior Manager Public Affairs and Traffic Safety Aaa Northeast, Hartford Courant, 10 Aug. 2025

Word History

Etymology

Middle English slugge, perhaps alteration of slicche mud, slush; akin to Old High German slīh mire

First Known Use

15th century, in the meaning defined at sense 1

Rhymes for sludge

• budge
• drudge
• frage
• fudge
• grudge
• judge
• mudge
• nudge
• rudge
• smudge
• trudge
• adjudge

Kids Definition

sludge

noun

ˈsləj 

1

: mud, mire

2

: a muddy or slushy mass

especially : solid matter produced by water and sewage treatment processes

sludgy

ˈsləj-ē 

adjective

Medical Definition

sludge

1 of 2 noun

ˈsləj 

: a semisolid precipitated mass or deposit

biliary sludge

especially : sludged blood

sludge

2 of 2 intransitive verb

sludged; sludging

: to form sludge

positions that cause blood to sludge

—L. K. Altman