but once

• adj. 只有一次

but once的用法和样例：

例句

1. Christmas come but once a year.
   人生得意须尽欢。
2. A man can die but once.
   人生只有一回死。
3. I made slow time down the steps but once on the flat I was all right.
   我慢慢地下着楼梯，但当我一踏上平地时，我就不要紧了。