(a.) Incapable of being passed over, surmounted, or overcome; insuperable; as, insurmountable difficulty or obstacle.

beyond one impassable impracticable impractical indomitable inoperable insuperable invincible too much for unachievable unattainable uncompassable unconquerable undoable uneffectible unnegotiable unperformable unrealizable unsurmountable unworkable