plural vs dual

plural is a noun but dual is not a noun.

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

plural (noun)	dual (noun)
the form of a word that is used to denote more than one

plural (adjective)	dual (adjective)
grammatical number category referring to two or more items or units	consisting of or involving two parts or components usually in pairs
composed of more than one member, set, or kind	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