sludge vs goo

sludge and goo both are nouns.

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

As nouns, sludge and goo are synonyms defined as:

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

sludge (noun)	goo (noun)
any thick, viscous matter	any thick, viscous matter
the precipitate produced by sewage treatment