extemporise vs ad-lib

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

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

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

Other synonyms of extemporise include extemporize, improvise, improvize.

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

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

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