1. 逐步的增长
A build-up is a gradual increase in something.
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e.g. There has been a build-up of troops on both sides of the border...
边境两边都在集结兵力。
e.g. The disease can also cause a build up of pressure in the inner ear leading to severe earache.
该疾病还会引起内耳的压力增加，从而导致剧烈的耳痛。
2. （对某活动的）宣传，造舆论
The build-up to an event is the way that journalists, advertisers, or other people talk about it a lot in the period of time immediately before it, and try to make it seem important and exciting.
e.g. We should wait at least until winter before we start the build-up to Christmas...
我们至少要等到冬天再开始着力营造圣诞节的气氛。
e.g. The exams came, almost an anticlimax after the build-up that the students had given them.
在学生们一番忙碌准备之后，随之而来的考试却出乎意料地平淡。