sludge vs guck

sludge and guck both are nouns.

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

As nouns, sludge and guck are synonyms defined as:

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

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