residual vs residuary

residual is a noun but residuary is not a noun.

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

As adjectives, residual and residuary are synonyms defined as:

residual (noun)	residuary (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

residual (adjective)	residuary (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)