to back somebody up,就是用背把某人扛起来,很容易想到是支持某人的意思。Back这里用作动词,实际上,back做动词本来就有支持的意思,常常指提供具体的帮助以支持. 例如:The company backed its candidate with a $1,000-a-plate dinner. 实际上,at one’s back 或者 at the back of sb.也表示支持某人的意思,用了back的名词形式。但是值得注意的是get one's back up虽然形式同back sb. up非常像, 却是令人不快的意思,就是说惹得别人背过身去了,那就是让别人不高兴了,例如:Tom got his back up when I said he was wrong. 好了,我们还是回到今天的习语back someone up吧。
Example
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Lisa: How was today’s meeting? Did the boss cast endless questions to you and you were left like a perfect idiot?
Tom: What are you talking about?! He backed me up in the meeting and said that my idea was good.