improvise

Concise Oxford English Dictionary © 2008 Oxford University Press:
improvise/ˈɪmprəvʌɪz/

▶verb

• 1 create and perform (music, drama, or verse) spontaneously or without preparation.

• 2 produce or make (something) from whatever is available.

– derivatives
improvisation noun,
improvisational adjective,
improvisatorial adjective,
improvisatory adjective,
improviser noun.

– origin C19 (earlier (C18) as improvisation): from Fr. improviser or Ital. improvvisare, from improvviso ‘extempore’.