once

1. ADV If something happens once, it happens one time only. 一次[ADV with v]

I met Miquela once, briefly. 我见过蜜凯拉一次，时间很短。

Since that evening I haven't once slept through the night. 自那晚之后，我再也没睡过一次囫囵觉。

2. PRON Once is also a pronoun. 一次['the/this' PRON]

"Have they been to visit you yet?"—"Just the once, yeah."

“他们已经去看过你了吗？”— “来过，就那一次。”

3. ADV 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. 每隔…一次[ADV 'a' n]

Lung cells die and are replaced about once a week. 肺细胞约每周死亡、更新一次。

4. ADV If something was once true, it was true at some time in the past, but is no longer true. 从前

Her parents once ran a shop. 她父母从前开过一家商店。

I lived there once myself, before I got married. 我从前自己住在那儿，没结婚前。

5. ADV If someone once did something, they did it at some time in the past. 曾经[ADV with v]

I once went camping at Lake Michigan with a friend. 我曾和一个朋友去密执安湖野营。

We once walked across the frozen pond at two in the morning. 我们曾在凌晨2点徒步横穿冰冻的池塘。

6. CONJ If something happens once another thing has happened, it happens immediately afterward. 一…就

The decision had taken about 10 seconds once he'd read a market research study. 他读完一份市场调研报告后，10秒钟就做出了决定。

7. PHRASE If something happens all at once, it happens suddenly, often when you are not expecting it to happen. 突然

All at once there was someone knocking on the door. 突然有人敲门。

8. PHRASE If you do something at once, you do it immediately. 立刻

I have to go at once. 我得马上走。

Remove from the heat, add the parsley, toss and serve at once. 从火上端下来，加入香芹，搅拌后立刻上桌。

9. PHRASE If a number of different things happen at once or all at once, they all happen at the same time. 同时

You can't be doing two things at once. 你不能同时做两件事。

10. PHRASE For once is used to emphasize that something happens on this particular occasion, that it has never happened before, and may never happen again. 就此一次[强调]

For once, Dad is not complaining. 就这一次，爸爸没有抱怨。

11. PHRASE If something happens once again or once more, it happens again. 再一次

Amy picked up the hairbrush and brushed her hair once more. 艾米拿起梳子，又梳了一遍头发。

12. PHRASE If something happens once and for all, it happens completely or finally. 最终地[强调]

We have to resolve this matter once and for all. 我们必须彻底解决这件事情。

13. PHRASE If something happens once in a while, it happens sometimes, but not very often. 偶尔

Your body, like any other machine, needs a full service once in a while. 你的身体就像其他机器一样，偶尔也需要一次全面保养。

14. PHRASE If you have done something once or twice, you have done it a few times, but not very often. 一两次; 几次

I visited once or twice. 我参观过一两次。

Once or twice she had caught a flash of interest in William's eyes. 有一两次，她捕捉到威廉眼中一闪的关注。