once

adv.

1. 仅一次；一次
   on one occasion only; one time
   1. I've only been there once.
      我只去过那里一次。
   2. He cleans his car once a week.
      他每周洗一次汽车。
   3. She only sees her parents once every six months.
      她每半年才探望一次父母。
   4. He only did it the once .
      这种事儿他仅仅干过一次。
2. 曾；曾经
   at some time in the past
   1. I once met your mother.
      我曾经见过你母亲。
   2. He once lived in Zambia.
      他曾在赞比亚生活过。
   3. This book was famous once, but nobody reads it today.
      这本书曾名噪一时，但现在却无人问津。
3. （用于否定句、疑问句和if后）曾，根本
   used in negative sentences and questions, and after if to mean ‘ever’ or ‘at all’
   1. He never once offered to help.
      他从没有主动提出过帮忙。
   2. If she once decides to do something, you won't change her mind.
      她一旦决定干什么，谁也改变不了她的主意。

conj.

1. 一…就；一旦；当…时候
   as soon as; when
   1. We didn't know how we would cope once the money had gone.
      一旦钱花光了，我们就不知道该怎么办了。
   2. The water is fine once you're in!
      你一旦下了水，就会觉得水里挺舒适。

1. ADV 一次；一回
   If something happens once, it happens one time only.
   1. I met Wilma once, briefly...
      我曾经和威尔玛有过短短的一面之缘。
   2. Since that evening I haven't once slept through the night...
      从那天晚上之后，我没有睡过一次安稳觉。
   3. Mary had only been to Manchester once before.
      玛丽以前只去过一次曼彻斯特。
   4. Once is also a pronoun.
      
   5. 'Have they been to visit you yet?' — 'Just the once, yeah.'...
      “他们来看过你吗？”——“来过，就一次。”
   6. Listen to us, if only this once.
      听我们的吧，哪怕就这么一次。
2. ADV （与后接day, week, month等的a连用）（每…）一次，（每…）一回
   You use once with 'a' and words like 'day', 'week', and 'month' to indicate that something happens regularly, one time in each day, week, or month.
   1. Lung cells die and are replaced about once a week...
      肺细胞约每周新老更替一次。
   2. We arranged a special social event once a year to which we invited our major customers.
      我们每年举办一次专门的社交活动，邀请重要客户出席。
3. ADV （与后接day, week, year等的every连用）（每隔…）一次，（每隔…）一回
   You use once with 'every' and words like 'day', 'week', and 'year' to indicate that something happens a specified number of times and on a regular basis.
   1. The patient was seen for follow-up visits once every three months...
      这位病人每三个月接受一次随访就诊。
   2. My daughter comes to visit me once every fortnight.
      我女儿每两周来看我一次。
4. ADV 曾经，一度（状况如此）
   If something was once true, it was true at some time in the past, but is no longer true.
   1. The culture minister once ran a theatre...
      这位文化部长曾经经营过一家剧院。
   2. I lived there once myself, before I got married...
      我结婚前曾独自在那儿住过。
   3. The house where she lives was once the village post office...
      她现在住的房子曾经是村里的邮局。
   4. My memory isn't as good as it once was.
      我的记性赶不上从前了。
   5. ...an undulating park, once lovely but now ruined by new buildings.
      曾经景色秀美、而今被新建筑糟蹋得面目全非的高低错落的庭园
5. ADV 曾经（做过某事）
   If someone once did something, they did it at some time in the past.
   1. I once went camping at Lake Darling with a friend...
      我曾和一位朋友在达令湖畔露营。
   2. We once walked across London at two in the morning...
      我们曾在凌晨两点步行穿过伦敦。
   3. Diana had taken that path once.
      黛安娜曾走过那条路。
6. CONJ-SUBORD 一旦…（就…); 一…（就…）
   If something happens once another thing has happened, it happens immediately afterwards.
   1. The decision had taken about 10 seconds once he'd read a market research study...
      在他看过一份市场调研报告后大概10秒钟就作出了决定。
   2. Once customers come to rely on these systems they almost never take their business elsewhere...
      顾客一旦依赖上这些系统，几乎就不会光顾其他商家。
   3. Once inside her apartment she felt an urge to brush her teeth.
      一回到自己的公寓，她就有一种想要刷牙的冲动。
7. PHRASE 突然；忽然
   If something happens all at once, it happens suddenly, often when you are not expecting it to happen.
   1. I feel terribly sleepy all at once...
      我突然觉得特别困。
   2. All at once there was someone knocking on the door.
      忽然有人敲门。
8. PHRASE 立即；马上
   If you do something at once, you do it immediately.
   1. I have to go, I really must, at once...
      我得走了，我真的必须马上就走。
   2. Remove from the heat, add the parsley, toss and serve at once...
      端离炉子，加上欧芹，颠起翻面后就立刻上桌。
   3. The audience at once greeted him warmly.
      观众立即对他作出了热情的反应。
9. PHRASE 同时；一起
   If a number of different things happen at once or all at once, they all happen at the same time.
   1. You can't be doing two things at once...
      不能一心二用。
   2. No bank could ever pay off its creditors if they all demanded their money at once...
      如果所有的储户同时要求提取存款，没有哪家银行能办得到。
   3. She seems at once feminine and able to cope in a man's world.
      她看起来既有女人味，又能在男人的世界里游刃有余。
10. PHRASE 就此一次；破例一次
    For once is used to emphasize that something happens on this particular occasion, especially if it has never happened before, and may never happen again.
    1. For once, dad is not complaining...
       爸爸这次破天荒地没有抱怨。
    2. His smile, for once, was genuine.
       只有这一次，他真诚地笑了。
11. PHRASE 又一次；再次
    If something happens once again or once more, it happens again.
    1. Amy picked up the hairbrush and smoothed her hair once more...
       埃米拿起发梳，再次将头发梳理整齐。
    2. Once again an official inquiry has spoken of weak management and ill-trained workers.
       官方调查又一次提到了管理不力与工人缺乏训练的问题。
12. PHRASE 彻底地；一劳永逸地
    If something happens once and for all, it happens completely or finally.
    1. We have to resolve this matter once and for all...
       我们必须彻底解决这一问题。
    2. If we act fast, we can once and for all prevent wild animals in Britain from suffering terrible cruelty.
       如果我们迅速采取行动，就可以一劳永逸地使英国的野生动物免受残忍的虐待。
13. PHRASE 偶尔；间或
    If something happens once in a while, it happens sometimes, but not very often.
    1. Earrings need to be taken out and cleaned once in a while.
       耳环要偶尔取出来清洗一下。
    2. Once in a while she phoned him.
       她间或会给他打个电话。
14. PHRASE 一两次；几次
    If you have done something once or twice, you have done it a few times, but not very often.
    1. I popped my head round the door once or twice...
       我有几次头撞到了门上。
    2. Once or twice she had caught a flash of interest in William's eyes...
       有那么一两次，她发现威廉的眼睛里流露出一丝感兴趣的神色。
    3. She gazed up at him, blinking once or twice, apparently surprised at his cleverness.
       她抬头注视着他，偶尔才眨一下眼睛，显然对他的聪明才智颇为惊讶。
15. PHRASE （常用于儿童故事的开头）从前，很久以前
    Once upon a time is used to indicate that something happened or existed a long time ago or in an imaginary world. It is often used at the beginning of children's stories.
    1. 'Once upon a time,' he began, 'there was a man who had everything.'...
       “很久很久以前，”他开始说道，“有这么一个人，他应有尽有。”
    2. Once upon a time, asking a woman if she has a job was quite a straightforward question.
       从前，问一位女性是否有工作是个相当简单直接的问题。
16. once in a blue moon → see: moon

1. I met Wilma once, briefly
   我曾经和威尔玛有过短短的一面之缘。
2. Since that evening I haven't once slept through the night
   从那天晚上之后，我没有睡过一次安稳觉。
3. Mary had only been to Manchester once before.
   玛丽以前只去过一次曼彻斯特。
4. Lung cells die and are replaced about once a week
   肺细胞约每周新老更替一次。
5. We arranged a special social event once a year to which we invited our major customers.
   我们每年举办一次专门的社交活动，邀请重要客户出席。
6. The patient was seen for follow-up visits once every three months
   这位病人每三个月接受一次随访就诊。
7. My daughter comes to visit me once every fortnight.
   我女儿每两周来看我一次。
8. The culture minister once ran a theatre
   这位文化部长曾经经营过一家剧院。
9. I lived there once myself, before I got married
   我结婚前曾独自在那儿住过。
10. The house where she lives was once the village post office
    她现在住的房子曾经是村里的邮局。
11. My memory isn't as good as it once was.
    我的记性赶不上从前了。
12. I once went camping at Lake Darling with a friend
    我曾和一位朋友在达令湖畔露营。
13. We once walked across London at two in the morning
    我们曾在凌晨两点步行穿过伦敦。
14. Diana had taken that path once.
    黛安娜曾走过那条路。
15. The decision had taken about 10 seconds once he'd read a market research study
    在他看过一份市场调研报告后大概10秒钟就作出了决定。
16. Once customers come to rely on these systems they almost never take their business elsewhere
    顾客一旦依赖上这些系统，几乎就不会光顾其他商家。
17. Once inside her apartment she felt an urge to brush her teeth.
    一回到自己的公寓，她就有一种想要刷牙的冲动。
18. I feel terribly sleepy all at once
    我突然觉得特别困。
19. All at once there was someone knocking on the door.
    忽然有人敲门。
20. I have to go, I really must, at once
    我得走了，我真的必须马上就走。
21. Remove from the heat, add the parsley, toss and serve at once
    端离炉子，加上欧芹，颠起翻面后就立刻上桌。
22. The audience at once greeted him warmly.
    观众立即对他作出了热情的反应。
23. You can't be doing two things at once
    不能一心二用。
24. No bank could ever pay off its creditors if they all demanded their money at once
    如果所有的储户同时要求提取存款，没有哪家银行能办得到。
25. For once, dad is not complaining
    爸爸这次破天荒地没有抱怨。
26. Amy picked up the hairbrush and smoothed her hair once more
    埃米拿起发梳，再次将头发梳理整齐。
27. We have to resolve this matter once and for all
    我们必须彻底解决这一问题。
28. Earrings need to be taken out and cleaned once in a while.
    耳环要偶尔取出来清洗一下。
29. I popped my head round the door once or twice
    我有几次头撞到了门上。
30. 'Once upon a time,' he began, 'there was a man who had everything.'
    “很久很久以前，”他开始说道，“有这么一个人，他应有尽有。”

adv.

all at once

• 突然；骤然；忽然
  suddenly
  1. All at once she lost her temper.
     她突然大发脾气。
• 一起；同时
  all together; at the same time
  1. I can't do everything all at once─you'll have to be patient.
     我不能万事一把抓呀。你可急不得。

at once

• 立即；马上
  immediately; without delay
  1. Come here at once!
     马上到这里来！
• 同时
  at the same time
  1. Don't all speak at once!
     大家不要同时讲！
  2. I can't do two things at once.
     我不能同时做两件事。

(just) for once

just this once

• 仅此一次（与通常情况对比而言）
  on this occasion (which is in contrast to what happens usually)
  1. Just for once he arrived on time.
     只有这一次他按时到了。
  2. Can't you be nice to each other just this once?
     难道你们就不能彼此客气哪怕一次？

going once, going twice, sold

going once, going twice, sold

once again

once more

• 再一次；再次
  one more time; another time
  1. Once again the train was late.
     火车又一次晚点了。
  2. Let me hear it just once more.
     让我再听一遍。

once a…, always a…

• （表示一个人不能改变） 一次为…便永远是…
  used to say that sb cannot change
  1. Once an actor, always an actor.
     一朝从艺，永为艺人。

once and for all

• 最终地；最后地；彻底地；一次了结地
  now and for the last time; finally or completely
  1. We need to settle this once and for all.
     我们需要把这事一次解决。

once bitten, twice shy

• 一朝被蛇咬，十年怕井绳
  after an unpleasant experience you are careful to avoid sth similar

once in a blue moon

• 极少地；难得地；破天荒地
  very rarely

(every) once in a while

• 偶尔地；间或
  occasionally

once or twice

• 一两次；几次
  a few times
  1. I don't know her well, I've only met her once or twice.
     我跟她不很熟；我只见过她一两次。

once too often

• 侥幸难再
  used to say that sb has done sth wrong or stupid again, and this time they will suffer because of it
  1. You've tried that trick once too often.
     你故技重施，可这次再逃不脱了。

once upon a time

• （用于故事的开头）从前，很久以前
  used, especially at the beginning of stories, to mean ‘a long time in the past’
  1. Once upon a time there was a beautiful princess.
     从前，有一位美丽的公主。

adv

1. on one occasion
   1. once I ran into her

   Synonym:    one timein one case

2. at a previous time
   1. at one time he loved her
   2. her erstwhile writing
   3. she was a dancer once

   Synonym:    formerlyat one timeerstwhileerst

3. as soon as
   1. once we are home, we can rest