residuary vs residual

residuary is not a noun while residual is a noun.

Word	Noun	Adjective	Verb	Adverb
residuary	No	Yes	No	No
residual	Yes	Yes	No	No

As adjectives, residuary and residual are synonyms defined as:

residuary (noun)	residual (noun)
	(often plural) a payment that is made to a performer or writer or director of a television show or commercial that is paid for every repeat showing
	something left after other parts have been taken away

residuary (adjective)	residual (adjective)
relating to or indicating a remainder	relating to or indicating a remainder
entitled to the residue of an estate (after payment of debts and specific gifts)