Webster's Revised Unabridged Dictionary · 1913

Improvise

Improvise , transitive verb

[French improviser, it. improvvisare, from improvviso unprovided, sudden, extempore, Latin improvisus; pref. im- not + provisus foreseen, provided. See Proviso.]

1.
To compose, recite, or sing extemporaneously, especially in verse; to extemporize; also, to play upon an instrument, or to act, extemporaneously.
2.
To bring about, arrange, do, or make, immediately or on short notice, without previous preparation and with no known precedent as a guide.
Charles attempted to improvise a peace. — Motley
3.
To invent, or provide, offhand, or on the spur of the moment; as, he improvised a hammer out of a stone.

Improvise , intransitive verb

To produce or render extemporaneous compositions, especially in verse or in music, without previous preparation; hence, to do anything offhand.