rainy 是“下雨的”，day是“日子” ，那么rainy d

a rainy day

A rainy day除了字面上表示天气的意思，还表示“不如意的日子”，“穷困的日子”。

例：

I know you wanna buy a new TV, but you should really save that money for a rainy day.

我知道你很想买台新电视，但你真应该把这笔钱存下来以备不时之需。

这里要注意

save/keep money for a rainy day

可以表示

to save money for a time when it might be needed unexpectedly

存钱以备不时之需;有备无患;未雨绸缪

例：

Luckily she had saved some money for a rainy day.

幸好她未雨绸缪早有准备。