unprepared vs ad-lib

unprepared is not a noun while ad-lib is a noun.

Word	Noun	Adjective	Verb	Adverb
unprepared	No	Yes	No	No
ad-lib	Yes	Yes	Yes	No

unprepared (noun)	ad-lib (noun)
	remark made spontaneously without prior preparation

unprepared (adjective)	ad-lib (adjective)
without preparation; not prepared for	with little or no preparation or forethought
	said or done without having been planned or written in advance

unprepared (verb)	ad-lib (verb)
	perform without preparation