The Collaborative International Dictionary
Insupposable
Insupposable \In`sup*pos"a*ble\, a. Incapable of being supposed; not supposable; inconceivable.
Wiktionary
insupposable
a. Incapable of being supposed; inconceivable.
Usage examples of "insupposable".
It wouldn't for such a spectator have been altogether insupposable that, each so finely brown and so sharply spare, each confessing so to dents of surface and aids to sight, to a disproportionate nose and a head delicately or grossly grizzled, they might have been brother and sister.