/wen; [US] hwen; hwɛn/
interrog adv at what time; on what occasion 什么时候; 什么场合
*When can you come? 您什么时候能来?
* When did he die? 他是什么时候死的?
* I don't know when he died. 我不知道他是什么时候死的.
* When were you living in Spain? 您是什么时候住在西班牙的?
* Since when has he been missing? 他是从什么时候失踪的?

rel adv 关系副词
1 (used after time, day, month, etc 用于time、day、month等之後) at or on which 在那时; 其时
*Sunday is the day when very few people go to work. 星期日是没什么人上班的日子.
* There are times when I wonder why I do this job. 有时候我也不明白我为什么要做这个工作.
* It was the sort of morning when everything goes wrong. 那天上午就是那样, 事事不顺心.
2 at which time; on which occasion 在那时; 当时; 当场
*The Queen's last visit was in May, when she opened the new hospital. 女王上次来访是在五月份, 她那时主持了这座医院的落成典礼.

conj
1 at or during the time that 在...时; 当...时
*It was raining when we arrived. 我们到的时候正在下雨.
* When he saw her, he waved. 他一看见她就摆了摆手.
* When visiting London I like to travel by bus. 我游览伦敦时喜欢坐公共汽车.
2 since; considering that 既然; 考虑到
*How can they learn anything when they spend all their spare time watching television? 他们把所有的空闲时间都用来看电视了, 还能学什么东西呢?

adv, conj, pron
[Language: Old English;Origin: hwanne, hwenne]
at what time
　When are we leaving?
　When did you first meet Dr Darnall?
　When will the work be finished?
　I don't know when I'll see her again.
when to do sth
　I'll tell you when to stop.
at or during the time that something happens
　Leonard was nine when his father died.
　When the family came here from Russia, they were penniless.
　When he was in the airforce he flew Tornado jets.
after or as soon as something happens
　When the meal was finished, Rachel washed up and made coffee.
　I'll phone you again when I get home.
used to mention a type of event or situation when talking about what happens on occasions of that type
　When lead is added to petrol, it improves the car's performance.
　When mixed with water the powder forms a smooth paste.
　He always wears glasses except when playing football.
used to show which particular time or occasion you are talking about
　The best moment was when Barnes scored the winning goal.
　There are times when I hate him.
the day/time/afternoon etc when
　She remembered the day when Paula had first walked into her office.
by/since when
before or since which time
　The baby is due in May, by when the new house should be finished.
　That was written in 1946, since when the education system has undergone great changes.
since when ...?
spoken used to show that you are very surprised or angry
　Since when have you been interested in my feelings?
even though something is true
　Why does she steal things when she could easily afford to buy them?
used to introduce a fact or statement that makes something seem surprising
　When you consider that the airline handled 80 million passengers last year, the accident figures are really very small.