boxcars vs plural form

boxcars and plural form both are nouns.

Word	Noun	Adjective	Verb	Adverb
boxcars	Yes	No	No	No
plural form	Yes	No	No	No

boxcars (noun)	plural form (noun)
(usually plural) an expression used when two dice are thrown and both come up showing six spots	the form of a word that is used to denote more than one