Wiktionary
a. Not defeatable; impossible to defeat. n. Something that has an undefeatable quality.
Wikipedia
Undefeatable is a 1994 martial arts movie starring Cynthia Rothrock and directed by Godfrey Ho (using the pseudonym Godfrey Hall). The picture was a Hong Kong production, but filmed in English on location in the United States. An alternate version of the film, titled Bloody Mary Killer, was released for the Asian markets.
Usage examples of "undefeatable".
Beneath Luis the turret kept turning, the huge turret with the undefeatable cannon.
Little, weak, semi-feudal, silly, comic opera Ochoa, out there in the middle of nowhere gobbling fish and drinking wine, had, in a semitech environment, defeated the undefeatable, stopped the unstoppable, and, best of all, humiliated the arrogant bastards.