Definition of "extemporaneous"

My speeches in Great Britain were wholly extemporaneous, and I may not always have been so guarded in my expressions, as I otherwise should have been. I was ten years younger then than now, and only seven years from slavery.

1855, Frederick Douglass, My Bondage and My Freedom. […], New York, Auburn, N.Y.: Miller, Orton & Mulligan […]

“Who the devil is there in Ramilly County,” muttered Amory aloud, “who would deliver Verlaine in an extemporaneous tune to a soaking haystack?”

1920 April, F[rancis] Scott Fitzgerald, “Young Irony”, in This Side of Paradise, New York, N.Y.: Charles Scribner’s Sons, book II (The Education of a Personage), page 241

The lovely words of a prepared speech, however, cannot erase extemporaneous words and deeds, thousands of them, that have run contrary to those aspirations.

2017 March 1, The Lead with Jake Tapper‎, spoken by Jake Tapper, via CNN