O 

of course当然

off and on断断续续地，间歇地，有时

off duty下班

on duty上班

on a large scale大规模地

on a small scale小规模地

on account of因为，由于

on average平均;通常;一般

on behalf of代表，为了

I paid the money on your behalf.

我替你付了钱。

Don‘t trouble to do it on my behalf.

不要为了我去麻烦了。

on board 在船(车、飞机)上

on business办事;因公出差

on condition that如果;在…条件下

on duty值班，当班

on earth地球上，世界上;究竟;到底

on foot步行 (november decemberoctoderseptember)

on guard站岗，值班

on hand在手边;临近

on occasion(s)有时，间或地

on (the) one hand一方面

on one’s guard警惕，提防

on one’s own独自，独立地

on purpose故意，有意

on sale上市，出售;减价，贱卖

on schedule按时间表，准时 on time准时 in time及时

on second thoughts经重新考虑

on the average平均，通常

on the contrary正相反

on the grounds of根据，以…为理由

on the other hand另一方面

on the point of即将…的时候

on the side作为兼职，作为副业;私下

an evening job to bring in a little money on the side.

He makes a little money on the side by not reporting all his income to the taxman.

on the spot在现场，当场

on the whole总的看来，大体上，基本上

on time准时

once again / more再一次

once for all永远地，一劳永逸地

once in a while偶尔，有时

one another互相 =each other互相

or else否则，要不然

or so大约

other than除…之外，除非

There‘s nobody here other than me.

除了我这里没别人。

out of越出…之外;从…里面(=from);离开;由于;没有

out of breath喘不过气来，上气不接下气

out of date过时的，落后的

out of doors在户外

out of order发生故障，失调，(工作)不正常

out of place不适当的，不相称

out of practice 久不练习，荒疏

out of question无疑 =beyond question

out of sight看不见=invisible

out of the question不可能的，办不到的

Their victory is out of the question: they’ve lost too many men.

out of touch不联系，不接触

over and over反复，再三 over and over again

owing to由于;因为

They could not cross the river owing to the flood. 由于洪水，他们不能过河。

Owing to the immediate danger of war, there will be an extraordinary meeting of

Parliament(congress) tonight. 由于即将发生的战争危险,今晚议会将召开特别会议。