once
adverb /wʌns/
/wʌns/
Idioms - on one occasion only; one time
仅一次；一次 - I've only been there once.
我只去过那里一次。 - He cleans his car once a week.
他每周洗一次汽车。 - She only sees her parents once every six months.
她每半年只探望一次父母。 - For optimum effect, these drops are used once daily.
为了达到最佳效果，这些滴剂每天使用一次。 - I had met Lou once before.
我以前见过娄一次。 - Last year the region received rain only once.
去年这个地区只下过一次雨。 - (informal) He only did it the once.
这种事儿他仅仅干过一次。 - Rome is a city you should visit at least once in your life.
罗马是一座你一生中至少应该去一次的城市。 - They meet once a week at a Paris café.
他们每周在巴黎咖啡馆见一次面。
- I've only been there once.
- at some time in the past
曾；曾经 - I once met your mother.
我曾经见过你母亲。 - He once lived in Zambia.
他曾在赞比亚生活过。 - 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。 - She remembers once travelling with her father to Kilkenny.
她记得有一次和父亲一起去基尔肯尼旅行。 - I famously once said that I was a fighter and not a quitter.
我有一句名言，我是一个斗士，不是一个半途而废的人。 - He once told an interviewer that his biggest regret was missing his father's funeral.
他曾告诉一位采访者，他最大的遗憾是错过了父亲的葬礼。 - It was once thought to be the best hotel in Europe.
它曾被认为是欧洲最好的酒店。
- I once met your mother.
- used in negative sentences and questions, and after if to mean ‘ever’ or ‘at all’
（用于否定句、疑问句和 if 后）曾，根本 - He never once offered to help.
他从没有主动提出过帮忙。 - 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。
- He never once offered to help.
- used with a preposition or another adverb to mean ‘as soon as somebody/something is/was’
一…就；一旦；当…时候 - Once inside the gate, Sam hurried up the path.
一进大门，萨姆就急忙跑上小路。
- Once inside the gate, Sam hurried up the path.
词源Middle English ones, genitive of one. The spelling change in the 16th cent. was in order to retain the unvoiced sound of the final consonant.
Idioms
all at once
- suddenly
突然；骤然；忽然 - All at once she lost her temper.
她突然大发脾气。
- All at once she lost her temper.
- all together; at the same time
一起；同时 - 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。
- I can't do everything all at once—you'll have to be patient.
at once
- immediately; without delay
立即；马上 - Come here at once!
马上到这里来！
- Come here at once!
- at the same time
同时 - Don't all speak at once!
大家不要同时讲！ - I can't do two things at once.
我不能同时做两件事。
- Don't all speak at once!
(just) for once | just this once
- (informal) on this occasion (which is in contrast to what happens usually)
仅此一次（与通常情况对比而言） - Just for once he arrived on time.
只有这一次他按时到了。 - 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？
- Just for once he arrived on time.
going once, going twice, sold (especially North American English)
(British English also going, going, gone)
- said by an auctioneer to show that an item has been sold
（拍卖师用语）一次，二次，成交
once again | once more
- one more time; another time
再一次；再次 - Once again the train was late.
火车又一次晚点了。 - Let me hear it just once more.
让我再听一遍。
- Once again the train was late.
once a…, always a…
- used to say that somebody cannot change
（表示一个人不能改变）一次为…便永远是… - Once an actor, always an actor.
一朝从艺，永为艺人。
- Once an actor, always an actor.
once bitten, twice shy
- (saying) after an unpleasant experience you are careful to avoid something similar
一朝被蛇咬，十年怕井绳
once (and) for all
- now and for the last time; finally or completely
最终地；最后地；彻底地；一次了结地 - We need to settle this once and for all.
我们需要把这事一次解决。
- We need to settle this once and for all.
once in a blue moon
- (informal) very rarely
极少地；难得地；破天荒地
(every) once in a while
- occasionally
偶尔地；间或 - Everybody makes a mistake once in a while.
每个人都偶尔会犯错误。
- Everybody makes a mistake once in a while.
once or twice
- a few times
一两次；几次 - 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。
- I don't know her well, I've only met her once or twice.
once too often
- used to say that somebody has done something wrong or stupid again, and this time they will suffer because of it
侥幸难再 - You've tried that trick once too often.
你故伎重施，可这次再逃不脱了。
- You've tried that trick once too often.
once upon a time
- used, especially at the beginning of stories, to mean ‘a long time ago in the past’
（用于故事的开头）从前，很久以前 - Once upon a time there was a beautiful princess.
从前，有一位美丽的公主。
- Once upon a time there was a beautiful princess.