From Longman Dictionary of Contemporary Englishunforgivableun‧for‧giv‧a‧ble /ˌʌnfəˈɡɪvəbəl◂ $ -fər-/ adjective FORGIVE#an unforgivable action is so bad or cruel that you cannot forgive the person who did it Patrick had deceived her, and that was unforgivable. the unforgivable sin of informing on your friends —unforgivably adverb
Examples from the Corpus
unforgivable• His betrayal was unforgivable.• On another occasion a relatively small misdemeanour proved unforgivable.• She thought his behaviour was unforgivable.• She thinks my leaving her alone with our parents is a great and unforgivable betrayal.• This is unforgivable in the realm of scientific methodology.• Franz, the egregiously angry Detective Andy Sipowicz, was his usual unforgivable / lovable self times 10.• I put down the pen, because this would be the great, unforgivable Miltonian sin.• What was unforgivable was that he had systematically lied to me - and I had let him do it.unforgivable sin• Marriage in his eyes is sacred; adultery the unforgivable sin.• Luke O'Malley had committed the unforgivable sin - he had informed on his friends.• Death is the unforgivable sin of modernity, and the modern world will have nothing to do with her. 