1. Descriptive of how something is incapable of being surmounted, passed over, or overcome: Because of many insurmountably demanding problems concerning the upcoming senior prom, the staff decided to postpone it until a later date.
2. Concerning how some physical obstacle is too great to be overcome: The hike to the peak of the very high mountain seemed to be insurmountably difficult and exhausting for Jenny who hadn't had much experience in mountain climbing.