unsupposable

unsupposable

(ˌʌnsəˈpəʊzəbəl)
adj
not able to be supposed
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in classic literature ?
It was unsupposable that Marilla was making fun of her, but Mrs.
It was unsupposable that he would ever marry; nobody ever had supposed it.