Douglas Harper's Etymology Dictionary
1879; see improvisation + -al (1).
Wiktionary
a. Having the nature of an improvisation.
Wikipedia
Usage examples of "improvisational".
We had a church choir from Alabama singing gospel music, and a high school band from Michigan playing a medley of favorite collegiate fight songs, and talented clones of the original stars nostalgically re-creating the Steve and Eydie Experience, and an improvisational comedy troupe from Los Angeles or someplace, and the New York Philharmonic under the baton of a twelve-year-old girl genius.
He held center stage, right at the seawall itself, performing unlilsely feats of juggling, general legerdemain, and Robin Williams-like improvisational comedy—.
He held center stage, right at the seawall itself, performing unlilsely feats of juggling, general legerdemain, and Robin Williams-like improvisational comedy-on a tightrope, balanced high above water that had not yet made up its mind whether it was Atlantic Ocean or Gulf of Mexico.