incidental expense vs plural

incidental expense and plural both are nouns.

Word	Noun	Adjective	Verb	Adverb
incidental expense	Yes	No	No	No
plural	Yes	Yes	No	No

incidental expense (noun)	plural (noun)
(frequently plural) an expense not budgeted or not specified	the form of a word that is used to denote more than one

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