underpants vs plural form

underpants and plural form both are nouns.

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

underpants (noun)	plural form (noun)
an undergarment that covers the body from the waist no further than to the thighs; usually worn next to the skin	the form of a word that is used to denote more than one