不相信的英文表达是"doubt"或"disbelief"。其来源可能源于古法语的"dubitare"，意思是"犹豫不定"。例句：

I have no doubt that he will succeed. (我毫不怀疑他会成功。)

The news of his death filled me with disbelief. (他死亡的消息让我难以置信。)