useful vs functional

useful and functional both are adjectives.

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

useful (adjective)	functional (adjective)
being of use or service	designed for or capable of a particular function or use
having a useful 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