in·con·ceiv·a·ble 
(ĭn′kən-sēvə-bəl)
(ĭn′kən-sēvə-bəl)adj.
1. Impossible to comprehend or grasp fully: inconceivable folly; an inconceivable disaster.
2. So unlikely or surprising as to have been thought impossible; unbelievable: an inconceivable victory against all odds.
in′con·ceiv′a·bili·ty, in′con·ceiva·ble·ness n.
in′con·ceiva·bly adv.