role vs functional

role is a noun but functional is not a noun.

Word	Noun	Adjective	Verb	Adverb
role	Yes	No	No	No
functional	No	Yes	No	No

role (noun)	functional (noun)
the actions and activities assigned to or required or expected of a person or group
normal or customary activity of a person in a particular social setting
what something is used for
an actor's portrayal of someone in a play

role (adjective)	functional (adjective)
	designed for or capable of a particular function or use
	involving or affecting function rather than physiology
	relating to or based on function especially as opposed to structure
	(of e.g. a machine) performing or capable of performing
	designed for or adapted to a function or use
	fit or ready for use or service