plural vs knuckles

plural and knuckles both are nouns.

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

plural (noun)	knuckles (noun)
the form of a word that is used to denote more than one	(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand

plural (adjective)	knuckles (adjective)
grammatical number category referring to two or more items or units
composed of more than one member, set, or kind