multiple vs dual

multiple is a noun but dual is not a noun.

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

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

multiple (adjective)	dual (adjective)
having or involving or consisting of more than one part or entity or individual	consisting of or involving two parts or components usually in pairs
	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