To descend to the lowest point possible, after which only a rise may occur
跌到谷底：跌到可能的最底点，在其后只有一个回升会发生
Sales of personal computers have bottomed out.
个人电脑的销售跌到了最底点
be the basic cause or origin of (something)
是…真正的起因（或根源）
he knew what was at the bottom of it—Jane wanted them to live together.
他知道真正的原因——简想和他生活在一起。
used to refer to the sudden collapse or failure of something
出现暴跌（或垮台）的局面
the bottom fell out of the market for classic cars.
高级轿车市场暴跌。
(informal)used to express friendly feelings towards one's companions before drinking
(非正式)干杯！
starting at the lower end or beginning of a hierarchy or process and proceeding to the top
从最底层做起；从头学起
we began to study history from the bottom up.
我们从头学历史。
find an explanation for (a mystery)
探明…的真相；弄清…的起因；寻到…的根子
cause (something) to collapse or fail suddenly
使突然坍塌（或失败）
a shortfall in supplies would knock the bottom out of the engineering industry.
物资供应不足会使机械建造业崩溃。
(informal, chiefly N. Amer.)used to state one's conviction that a particular thing is going to happen
(非正式，主 北美)深信，确信
you can bet your bottom dollar it'll end in tears.
可以确定，这要以眼泪收场。
Basically.
根本上