1. Number one 最重要的人(或事物);最好的人(或事物)
Many people consider themselves number one, the most important person.
很多人认为他们自己就是最好的，是最重要的一个人。
2. Look out for/ Take care of number one 先为自己着想，照顾自己的利益, 为自己打算
One and only 绝无仅有的;独一无二的;有名的
They are always looking out for number one and taking care of number one. It is as if they are the one and only person on Earth.
他们总是先为自己着想，只关心自己的利益，就好像他们是地球上唯一的人。
3. Pull a fast one 欺骗, 捣鬼
Jim only won the game because he pulled a fast one on his opponent.
吉姆因为跟对手耍了手段，才贏了比賽。
4. One in a million百万分之一，凤毛麟角，百里挑一，佼佼者
She's one in a million.
她是个百里挑一的人。
5. At one time 同时, 曾经
At one time we met frequently.
我们过去常见面。
6. Roll up into one 合为一体;兼于一身
She is a great person -- kind, thoughtful and intelligent -- all good qualities rolled up into one.
她是个很优秀的女人——善良，体贴，聪慧——集所有可贵品质于一身。
7. One good turn deserves another. 善须善报;要以德报德;好人应得好报。
If he does you a favor, you should do him a favor. One good turn deserves another.
如果他帮你的忙，那么你就应帮他的忙，以德报德嘛。
8. Be/go back to square one 退回起点, 从头再来
His papers were lost in the accident, so he had to go back to square one with the work.
他的论文在这次事故中弄丢了，只得从头再写。