Longman Dictionary of Contemporary English homepage

Date: 1600-1700
Origin: Probably from slush

sludge

 noun
     
Related topics: Nature, Industry
sludge [uncountable]
1DN soft thick mud, especially at the bottom of a liquid
2TI the solid substance that is left when industrial waste or sewage (=the liquid waste from toilets) has been cleaned
3TTC thick dirty oil in an engine
—sludgy adjective
Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.

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