extemporise vs improvise

extemporise and improvise both are verbs.

Word	Noun	Adjective	Verb	Adverb
extemporise	No	No	Yes	No
improvise	No	No	Yes	No

As verbs, extemporise and improvise are synonyms defined as:

Other synonyms of extemporise include ad-lib, extemporize, improvize.

extemporise (verb)	improvise (verb)
perform without preparation	perform without preparation
	manage in a makeshift way; do with whatever is at hand