Wiktionary
undreamable
a. Not dreamable; that cannot be dreamed.
Usage examples of "undreamable".
So Amina had found herself dreaming about an undreamable poet's face and waking with an unspeakable name on her lips.
No undreamable dreams about whether the headless, feetless torso hanging in the tree with a sign on it was her husband or Paul A.
Like the goblin steed of some impossible elf-knight, it flashed through the dim amber gloom on its undreamable mission!