Douglas Harper's Etymology Dictionary
1857, from transformation + -al (1).
Wiktionary
a. Of, pertaining to or leading to transformation
Wikipedia
Usage examples of "transformational".
His thirteen years with the monks in Tibet had taught him much about the wonders of vampiric physiognomy, the astounding supernatural plasticity that was not at all limited to the traditional European transformational varieties of bat, wolf, and mist.
By joint tasking and transformational processes, this situation can be deconflicted in a rapid and decisive manner.
I achieved only this: I proved that using the apparatus of the topological and transformational algebras would NOT enable one to solve the problem.
One of these (the one Arthur now came across) supposedly relates the experiences of one Veet Voojagig, a quiet young student at the University of Maximegalon, who pursued a brilliant academic career studying ancient philology, transformational ethics and the wave harmonic theory of historical perception, and then, after a night of drinking Pan Galactic Gargle Blasters with Zaphod Beeblebrox, became increasingly obsessed with the problem of what had happened to all the biros he'd bought over the past few years.