functional vs functioning

functional is not a noun while functioning is a noun.

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

functional (noun)	functioning (noun)
	process or manner of functioning or operating

functional (adjective)	functioning (adjective)
designed for or capable of a particular function or use	performing or able to perform its regular function
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