unpardonable
From Longman Dictionary of Contemporary Englishunpardonableun‧par‧don‧a‧ble /ʌnˈpɑːdnəbəl $ -ˈpɑːr-/ adjective formal FORGIVE#unpardonable behaviour is completely unacceptable SYN unforgivable an unpardonable offence —unpardonably adverbExamples from the Corpusunpardonable• That would be seen by many as an unpardonable failure that disqualifies him from having a second run.• To some it is even the ultimate treason against faith, the unpardonable sin.