一个星期用英语可以说作 "a week"。这个词本身就是由两个英文单词组合而成的，分别是 "a" 和 "week"。"a" 是英文的一个冠词，表示一个或一件东西，"week" 是英文中指一星期的单词。

例句：

I will see you in a week.

I need to finish this project within a week.

I haven't seen her in a week.

I'm going on vacation for a week.

I have a lot of work to do this week.