IPA: //ʌnˈfɔːɡɪvəbl//
KK: /ʌnˈfɔrɡɪvəbəl/
Describing something that is so bad or hurtful that it cannot be forgiven.
His actions were truly unforgivable, and many people were hurt by them.
Unforgivable → It is formed from "un-" (meaning not) and "forgivable" (from Old English "forgiefan", meaning to give up or pardon). The word "unforgivable" means something that cannot be pardoned or excused.
Think of 'not' ('un-') being able to 'pardon' ('forgivable') — that's why unforgivable means something that cannot be forgiven.