The Collaborative International Dictionary
Impassableness
Impassable \Im*pass"a*ble\, a. [Cf. Unpassable.]
Incapable of being passed; not admitting a passage; as, an
impassable road, mountain, or gulf.
--Milton. --
Im*pass"a*ble*ness, n. -- Im*pass"a*bly, adv.
Wiktionary
impassableness
n. The quality of being impassable.