plural vs Napier's rods

plural and Napier's rods both are nouns.

Word	Noun	Adjective	Verb	Adverb
plural	Yes	Yes	No	No
Napier's rods	Yes	No	No	No

plural (noun)	Napier's rods (noun)
the form of a word that is used to denote more than one	a set of graduated rods formerly used to do multiplication and division by a method invented by John Napier

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