extemporize vs ad-lib

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

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

As verbs, extemporize and ad-lib are synonyms defined as:

Other synonyms of extemporize include extemporise, improvise, improvize.

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

extemporize (adjective)	ad-lib (adjective)
	with little or no preparation or forethought
	said or done without having been planned or written in advance

extemporize (verb)	ad-lib (verb)
perform without preparation	perform without preparation
manage in a makeshift way; do with whatever is at hand