■on end 直立；连续地
The terrible sight made her hair stand on end. 那可怕的景象使她毛骨悚然。
It has been snowing for a week on end. 雪连续下了一周了。
■on file 存档
We have all your particulars on file. 我们已把你的全部资料存档。
The interviewer promised to keep my job application on file. 主持面试的人答应将我的工作申请存档。
■on fire 着火了
Wake up! The house is on fire! 快醒醒！房子着火啦！
Help! The frying’s on fire! 快来啊！平底锅着火了！
■on foot 徒步，步行；在进行中
Shall we go by car or on foot? 我们坐车去还是走路去？
A project is on foot to build a new tunnel. 建造一条新隧道的计划在着手进行中。
■on guard 值班，当班；警戒
The sentry is on guard. 那哨兵在担任警戒。
Two men are on guard at the door. 两人在门口站岗。
■on hand 在手上；在场
He always has his dictionary on hand when he studies. 他学习时总是把词典放在手边。
There is a teacher on hand to help during your private study periods. 自修课上有教师在场辅导。
■on holiday 在度假，在休假
The typist is away on holiday this week. 打字员本周休假。
They went on holiday last month. 他们上个月度假去了。
■on holidays 在节假日，在公休日
On holidays the railways put on special trains. 假日铁路增加专列。
Travel is very heavy here on holidays. 假日这里的交通很拥挤。
【注】注意on holidays 与on holiday 在含义上的区别。
■on impulse 一时冲动，一时心血来潮
He saw them get into the car and on an impulse he followed them. 他看见他们钻进汽车，一时冲动之下他跟了上去。
On impulse, I picked up the phone and rang my sister in
■on leave 在休假
He is coming home on leave of absence. 他将回家休假。
You cannot find John because he is on leave now. 你找不到约翰的，因为他正在休假。
■on line 在线，在网上；（按计划）在运转，在运行
You can book tickets on line. 你可以在线订票。
If there is a power failure, the emergency generators should come on line within 15 minutes. 如果出现停电，应急发电机将在15分钟内开始运行。
■on loan 借（来）
He has my car on loan. 他借了我的汽车。
I have the book on loan from the library. 我从图书馆借了这本书。
■on oath 发誓
Is she prepared to give evidence on oath? 他准备发誓作证吗？
I testify on oath that I have not noticed the accident. 我发誓声明我没有注意到这场事故。
■on occasion 偶尔，有时
I meet him on occasion at the club or in the theatre. 我有时在俱乐部或在戏院里遇到他。
He reads detective stories on occasion. 他偶尔阅读侦探小说。
■on offer 供出售的（尤指削价出售的）
There are only inferior on offer. 只有低档货出售。
Baked beans are on offer this week at the local supermarket. 当地超级市场本周烘豆罐头大减价。
■on order 定购中，定制中
The shoes are on order and will be shipped next week. 鞋子已经订购但尚未交付，下个星期就可以装运了。
The textbook you require is temporarily out of stock, but it’s on order. 您要买的教科书暂时没有货，但是已经订购了。
■on paper 在纸上；以书面形式；在理论上
The children drew the outline of flowers on paper, then colored them. 孩子们把花的轮廓画在纸上，然后涂上颜色。
Why don’t you set your ideas down on paper? 你怎么不把你的想法以书面形式写出来呢?
It’s a fine scheme on paper, but will it work in practice? 那计划从理论上看不错，不过实践上是否可行?
■on purpose 故意地，特意地
“You’ve torn a page out of my book!” “I’m sorry, I didn’t do it on purpose.” “我的书给你撕掉了一页啦！”“很对不起，我不是故意的。”
I came a bit early on purpose, to see if I could help you. 我特地早一点来，看看能不能帮你的忙。
■on request 一经要求
Catalogues are available on request. 备有目录供索取。
The library will lend you this book on request. 只要你提出要求，图书馆就借给你这本书
【注】其中的on 也可换成 upon。如：
A pamphlet will be sent on [upon] request. 小册子函索即寄。
■on record 正式记录的；公开发表的
Last summer was the wettest on record for 50 years. 刚过去的这个夏季是50年来记录中雨水最多的。
She’s on record as opposing the new law. 她反对这项新法律，这是有案可查的。
■on sale 出售，有售
Every article on view will be on sale. 每件展品都将出售。
This week’s edition is on sale now at your local newsagents. 本期周刊已公开发售，读者可向各报贩购买。