gunk vs sludge

gunk and sludge both are nouns.

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

As nouns, gunk and sludge are synonyms defined as:

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

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