alternative vs unconventional

alternative is a noun but unconventional is not a noun.

Word	Noun	Adjective	Verb	Adverb
alternative	Yes	Yes	No	No
unconventional	No	Yes	No	No

alternative (noun)	unconventional (noun)
one of a number of things from which only one can be chosen

alternative (adjective)	unconventional (adjective)
necessitating a choice between mutually exclusive possibilities	not conforming to accepted rules or standards
serving or used in place of another	not conventional or conformist
pertaining to unconventional choices	not conforming to legality, moral law, or social convention