residuum vs residue

residuum and residue both are nouns.

Word	Noun	Adjective	Verb	Adverb
residuum	Yes	No	No	No
residue	Yes	No	No	No

As nouns, residuum and residue are synonyms defined as:

residuum and residue: something left after other parts have been taken away

Other synonyms of residuum include balance, remainder, residual, rest.

residuum (noun)	residue (noun)
something left after other parts have been taken away	something left after other parts have been taken away
	matter that remains after something has been removed