goop vs sludge

goop and sludge both are nouns.

Word	Noun	Adjective	Verb	Adverb
goop	Yes	No	No	No
sludge	Yes	No	No	No

As nouns, goop and sludge are synonyms defined as:

Other synonyms of goop include goo, gook, guck, gunk, muck, ooze, slime.

goop (noun)	sludge (noun)
street names for gamma hydroxybutyrate	any thick, viscous matter
any thick, viscous matter	the precipitate produced by sewage treatment