functional vs usable

functional and usable both are adjectives.

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

As adjectives, functional and usable are synonyms defined as:

Other synonyms of functional include operable, operational, useable.

functional (adjective)	usable (adjective)
designed for or capable of a particular function or use	convenient for use or disposal
involving or affecting function rather than physiology	fit or ready for use or service
relating to or based on function especially as opposed to structure	capable of being put to use
(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