The Collaborative International Dictionary of English v.0.48:
Unsurmountable \Un`sur*mount"a*ble\, a. Insurmountable. --Locke. [1913 Webster]WordNet (r) 3.0 (2006):
unsurmountable adj 1: not capable of being surmounted or overcome; "insurmountable disadvantages" [syn: insurmountable, unsurmountable] [ant: surmountable] 2: incapable of being surmounted or climbed [syn: unsurmountable, unclimbable]