one是不定代詞，只表示數量為壹的單數名詞，而沒有限定，one可以加修飾語。
1、泛指人們或任何人：One must have a dream. 人壹定要有夢想。
2、用來避免重復已提到過的或是聽者已知的事物：I’d like an apple. Are you having one? 我想吃個蘋果，妳要壹個嗎？
3、表示某個不確定的人或物，相當於“不定冠詞+名詞”：I’d like one with a garden. 我想要壹座帶花園的。
4、表示“其中壹個”：Here are two apples. One is for Mary, the other is for Lily. 這裏有兩個蘋果，壹個給瑪麗，壹個給麗麗。
5、a one（舉止）有趣的人：Oh, you are a one! 哈，妳真是個活寶。
6、the one about sth 玩笑：Have you heard the one about Chrismas. 妳聽過那個關於聖誕節的笑話嗎？
7、be a one for (doing) sth（樂於）長於做某事的人：My brother is a one for fishing. 我哥哥很會釣魚。
8、固定短語：one after the other 依次地。one after another壹個接壹個地。
雙語例句：
1、Most tickets have been snapped up, so get cracking if you want?one.
大部分門票已被搶購壹空；所以，如果妳想弄壹張的話，得趕快行動了。
2、Voicemail was seen as?one?of the desktop conveniences of the electronic office.
語音郵件曾被看做是電子辦公室的桌面便利之壹。
3、No?one?had been there for months — everything was out of trim.
有好幾個月沒人去過那裏了—— 壹切都是亂糟糟的。
4、He was the bright?one?and everyone was sure he would go far.
他是個聰明人，大家都確信他會取得很大的成就。
5、It seems invidious to make special mention of?one?aspect of his work.
只強調他工作的壹個方面似乎不太公平。
6、I was witness to?one?of the most amazing comebacks in sprinting history.
我目睹了短跑歷史上壹次最令人稱奇的東山再起。
7、Since your daughter is?one?of my regular patients, I'm stretching a point.
由於妳的女兒常來我這裏看病，我就破壹次例。
8、A branch whipped across the screen and tore off?one?of the wipers.
樹枝劃過了擋風玻璃，刮斷了壹根擋風玻璃雨刷。