functional vs useful

functional and useful both are adjectives.

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

functional (adjective)	useful (adjective)
designed for or capable of a particular function or use	being of use or service
involving or affecting function rather than physiology	having a useful function
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