sludge
[noun]
Synonyms: sediment, mire, muck, mud, ooze, residue, silt, slime

[TahlilGaran] English Synonym Dictionary ▲

sludge /slʌdʒ/ noun [uncountable]
[Date: 1600-1700; Origin: Probably from slush]

1. soft thick mud, especially at the bottom of a liquid

2. the solid substance that is left when industrial waste or sewage (=the liquid waste from toilets) has been cleaned

3. thick dirty oil in an engine
—sludgy adjective

[TahlilGaran] Dictionary of Contemporary English ▲