residue vs residuum

residue and residuum both are nouns.

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

As nouns, residue and residuum are synonyms defined as:

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

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

residue (noun)	residuum (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