1 since /ˈsɪns/ preposition Learner's definition of SINCE
: in the time after (a specified time or event in the past) : from (a point in the past) until the present time自…以后，从…以来（就一直）；自从…以后 -
I haven't seen him since yesterday.从昨天起我就没见过他。
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I haven't eaten since breakfast.早饭后我就没吃过东西。
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Since the party, she has not spoken to him at all.自那次聚会以后，她没跟他说过一句话。
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The company has been in its present location since the beginning of the century.自本世纪初以来，这家公司就一直在现在这个地方。
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We've been waiting for you since 10 o'clock.我们从10点钟就开始等你了。
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We have been friends since [=ever since] college.我们从大学时候起就是朋友。
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The company started as a small local business 10 years ago and has grown a lot since then. [=within that time]这家公司十年前由一家小型地方公司起家，到现在发展壮大了很多。
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The house was built in 1919. Since that time [=from 1919 to the present], it has changed owners several times.这栋房屋建于1919年。此后数次易主。
since the year one
— see year
since when?
—
used to show that you are surprised and often angry, annoyed, or doubtful about what someone has said or done什么时候开始的，何曾（表吃惊、气愤、恼怒或怀疑） -
“I'm a vegetarian.” “Since when?”“我是素食主义者。”“什么时候开始的？”
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“You told me to do it.” “Since when did you start listening to me?”“你叫我做的。”“你什么时候开始听我的话了？”
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Since when is it okay to cheat?从什么时候开始可以骗人了？
2 since /ˈsɪns/ conjunction
2 since
/ˈsɪns/
conjunction
Learner's definition of SINCE
1
: in the period after the time when在…以后，从…以来（的一段时间） 2
: from the time in the past when自…以后，从…以来，自从…（就一直） -
I have wanted to be a pilot since [=ever since] I was a child.我从小就想当一名飞行员。
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He hasn't ridden a bike since he was a boy.他从小就没骑过自行车。
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(US) It has been over 10 years since I last visited Europe. = (Brit) It is over 10 years since I last visited Europe.距我上次访问欧洲已经有十多年了。
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They haven't won a championship since Truman was President.自杜鲁门任总统以来他们还没有赢得过冠军。
3
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used to introduce a statement that explains the reason for another statement既然；由于 -
Since you've finished all your chores, you may go out and play.既然活都干完了，你可以出去玩了。
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Should we invite someone else since he can't go?他无法赴约，我们是否应该另邀他人？
3 since /ˈsɪns/ adverb
Learner's definition of SINCE
1
: from a past time until now至今，自…以来（就一直） 2
: after a time in the past此后；之后 3
: before the present time此前；之前 — see also long since at 2long