inconceivable
//ˌɪnkənˈsiːvəbəl//
Adjective
inconceivableCanonical form
1
Not capable of being imagined or grasped mentally; unbelievable or impossible to comprehend.
It is inconceivable that such a mistake could happen.
2
Extremely unlikely or implausible; beyond the bounds of reasonable expectation.
It is inconceivable that such a small mistake could cause so much damage.