spontaneous vs ad-lib

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

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

As adjectives, spontaneous and ad-lib are synonyms defined as:

spontaneous and ad-lib: said or done without having been planned or written in advance

Other synonyms of spontaneous include unwritten.

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

spontaneous (adjective)	ad-lib (adjective)
happening or arising without apparent external cause	with little or no preparation or forethought
said or done without having been planned or written in advance	said or done without having been planned or written in advance

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