unauthentic vs counterfeit

unauthentic is not a noun while counterfeit is a noun.

Word	Noun	Adjective	Verb	Adverb
unauthentic	No	Yes	No	No
counterfeit	Yes	Yes	Yes	No

unauthentic (noun)	counterfeit (noun)
	a copy that is represented as the original

unauthentic (adjective)	counterfeit (adjective)
false or fake; not what it appears to be	not genuine; imitating something superior

unauthentic (verb)	counterfeit (verb)
	make a copy of with the intent to deceive