Wiktionary
unfulfillable
a. Not fulfillable.
Usage examples of "unfulfillable".
How could she blame him for this unfulfillable desire when she had a similar one of her own?
Yet who could have foretold such generosity and greatness of soul as was displayed by the lady Dianora in freely offering that which she had no reason to give but to honor a word she had thought unfulfillable, or by yourself in willingly abandoning a goal you had unswervingly sought and beggared yourself to achieve?
Was it possible that he must pay for that rash enthusiasm all his life by never hearing, year after year, anything but these unchanging, shrill, crazy exclamations and demands, which became progressively more impractical, meaningless, and unfulfillable as time went by?