Adjective : an impossible assignment. ,an impossible situation. ,an impossible plan.    From Dictionary.com. 

Annie's touchy pride, mingled with what Vassie frankly called her "impossibleness," made the situation hopeless, for the former quality would not let her efface herself, and the latter prevented her daughter being called upon.    From Wordnik.com.  [Secret Bread] Reference

Sorry guys, there won't be much 'impossibleness' out of my case design.    From Wordnik.com.  [bit-tech.net Feed] Reference

I'd say the successful "impossible goals" that were accomplished in spite of their 'impossibleness' had a few things in common.    From Wordnik.com.  [Genuine Curiosity by Dwayne Melancon] Reference

G-man is the more immediately endearing character, and yet Brite handles Rickey and his impossibleness in a way that makes you really feel for him too.    From Wordnik.com.  [I'm snatching a few moments] Reference

But his character did allow us all to vent about the impossibleness of mothers-in-law, and it taught us how to achieve the very best that divorce settlements have to offer.    From Wordnik.com.  [Archive 2006-05-01] Reference

And as he talked, steadily, interestingly, he was doing what Dag Daughtry never dreamed he was doing, and what made Kwaque, looking on, almost dream he was seeing because of the unrealness and impossibleness of it.    From Wordnik.com.  [CHAPTER XIX] Reference

You see Herman's written it very cleverly, emphasizing the problematic rather than the pros and cons of each choice--most of us would obviously prefer one or the other of these standpoints, but once she writes it this way, you have to listen to the impossibleness of the choice.    From Wordnik.com.  [I've just raced through] Reference

Suddenly the impossibleness of everything seemed to come over Amaryllis.    From Wordnik.com.  [The Price of Things] Reference

Daughtry never dreamed he was doing, and what made Kwaque, looking on, almost dream he was seeing because of the unrealness and impossibleness of it.    From Wordnik.com.  [Chapter 19] Reference