"Once" 是 "曾经" 的英文翻译。
来源：该词最早出现在古英语中，意思是 "一次" 或 "曾经"。
例句：
I once loved him, but now I can't stand him. (我曾经爱过他，但现在我不能忍受他。)
Once upon a time, there was a beautiful princess. (从前，有一位美丽的公主。)
We only have one chance, and that's now, once in a pfetime. (我们只有一次机会，那就是现在，一生中的一次机会。)