English Reference
noun · verb

sludge

n. · v.
US /ˈsɫədʒ/ UK /slˈʌdʒ/ sludge UK spelling sludged, sludges, sludging

  1. 01 B2 Upper Intermediate

    n.a thick, wet, and messy mixture of liquid and solid material, like mud or waste.

    n.a thick, semi-solid mixture of liquid and solid components, typically associated with industrial waste, sewage, or heavy mud.

    Simple

    The heavy rain turned the garden path into a mess of thick, black sludge.

    In context

    Environmental inspectors discovered that the factory had been illegally dumping toxic sludge into the local river system for years.

  2. 02 C1 Advanced AcademicTechnical

    n.annoying rules or paperwork that make it difficult and slow to get things done.

    n.institutional policies or bureaucratic hurdles that introduce unnecessary tedium and inefficiency into a process.

    Simple

    The new government website was full of sludge that made applying for a passport very difficult.

    In context

    Economists argue that administrative sludge in the healthcare system costs the country billions in lost productivity every year.

    Usage

    Often used in behavioral economics to describe the opposite of a 'nudge'.

  3. 03 C1 Advanced Informal Music

    n.a style of heavy metal music that is very slow, loud, and dark.

    n.a subgenre of heavy metal music, characterized by slow tempos, abrasive rhythms, and a pessimistic atmosphere.

    Simple

    He spent the evening listening to old sludge records in his room.

    In context

    The band's latest album is a masterclass in sludge, blending doom metal influences with a raw, aggressive production style.

    sludge metal
  4. 04 C2 Proficiency InformalDialect

    v.to sit or move in a heavy, lazy way.

    v.to slump, slouch, or move with a heavy, lethargic gait.

    Simple

    After the long hike, he just sludged down into the armchair and fell asleep.

    In context

    The exhausted commuters sludged toward the train platform, their heads bowed against the biting winter wind.

    slumptrudgeslouch
    perk upspring

Researchers say they detected banned chemicals in air, water, sediments, soils, snow and sludge, demonstrating their environmental persistence.

Phys.org· 24 Aug 2026

Meanwhile, another company is looking to harness the process to recycle carbon from sewage sludge.

Smithsonian Magazine· 6 Jul 2026

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.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin gem-pro *slikiz
Level C1 · Advanced
Frequency Frequent
Updated