dual vs multiple

dual is not a noun while multiple is a noun.

Word	Noun	Adjective	Verb	Adverb
dual	No	Yes	No	No
multiple	Yes	Yes	No	No

dual (noun)	multiple (noun)
	the product of a quantity by an integer

dual (adjective)	multiple (adjective)
consisting of or involving two parts or components usually in pairs	having or involving or consisting of more than one part or entity or individual
a grammatical number category referring to two items or units as opposed to one item (singular) or more than two items (plural)
having more than one decidedly dissimilar aspects or qualities