When someone makes a mistake that is unforgivable, it can be challenging to find the right words to describe the situation. Some synonyms for "not forgivable" could be irredeemable, unpardonable, inexcusable, indefensible, incriminating, or condemnable. These words all convey a sense of wrongdoing that cannot be forgiven or overlooked. Perhaps the action was too severe, too intentional, or too damaging to justify forgiveness. Whatever the case may be, the word choice used to describe such an act has a significant impact on how the situation is perceived by others. Therefore, it is essential to choose words that accurately reflect the gravity of the offense and communicate the severity of the situation.