Too painful, too unpleasant, or too difficult to bear. This is the top of the scale. Something uncomfortable you put up with; something painful you struggle through; something unendurable defeats you — you cannot keep taking it, and you have to escape, stop, or break. It is used for physical pain ('the pain in his back became unendurable'), and just as often for feelings and situations: grief, shame, loneliness, heat, waiting, the tension in a room. Notice one strange thing about it: people usually keep enduring the unendurable anyway. Writers use it precisely because the situation continues past the point where it should be possible — 'those unendurable weeks after the funeral'. So it often describes what someone has already lived through, not what stopped them. It is a formal, written word; you would meet it in a novel or a serious article, not usually in conversation. In speech an English speaker would say 'I couldn't take it any more', 'it was unbearable', or just 'it was too much'. Unbearable is the common twin and means the same thing — it is simply the one people actually say.

難以忍受的、忍無可忍的（程度到了頂點）。這是書面語，講話時英語母語者多半說 unbearable 或 I couldn't take it any more。