So bad that it cannot be forgiven. A pardon is an official forgiveness — a king pardons a prisoner — so an unpardonable act is one you refuse to let go of, however much the person apologises. You will hear it about behaviour more than about crimes: unpardonable rudeness, an unpardonable insult, unpardonable laziness from someone who should have known better. Here is the thing your dictionary may not tell you: in real life the word is very often used lightly, almost as a joke, about small things. 'I forgot her birthday — unpardonable, I know.' Using such a huge word for such a small fault is exactly the point; it shows you know it was rude while smiling about it. Reading the tone is everything. A judge saying 'unpardonable' means it. A friend at dinner saying 'unpardonable' is teasing you. It is a formal, slightly old-fashioned, rather literary word — in ordinary speech people say 'there's no excuse for it' — and 'unforgivable' is the more common everyday twin, meaning much the same thing but sounding less bookish.

不可原諒的、不可饒恕的。書面語、略帶老派；日常較常說 unforgivable。注意口語裡常拿它開玩笑，故意用重話講小事（「我忘了她生日，罪該萬死」）。