To improvise is defined as to do something on the spur of the moment.(verb)
An example of to improvise is someone having to give a speech without any notice.
See improvise in Webster's New World College Dictionary
Origin: Fr improviser < It improvvisare < improvviso, unprepared < L improvisus, unforeseen < in-, not + provisus, pp. of providere, to foresee, anticipate: see provide
See improvise in American Heritage Dictionary 4
verb im·pro·vised, im·pro·vis·ing, im·pro·vis·es verb, transitive
Origin: French improviser
Origin: , from Italian improvvisare
Origin: , from improvviso, unforeseen
Origin: , from Latin imprōvīsus
Origin: : in-, not; see in-1
Origin: + prōvīsus
Origin: , past participle of prōvidēre, to foresee; see provide.
Learn more about improvise