interest group vs plural

interest group and plural both are nouns.

Word	Noun	Adjective	Verb	Adverb
interest group	Yes	No	No	No
plural	Yes	Yes	No	No

interest group (noun)	plural (noun)
(usually plural) a social group whose members control some field of activity and who have common aims	the form of a word that is used to denote more than one

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