Example sentences
xià下yǔ雨le了。
It's raining.
míng明tiān天huì会xià下yǔ雨ma吗？
Will it rain tomorrow?
About this word
下 is "to descend, to fall" and 雨 is "rain". So 下雨 is literally "rain falls", with 雨 as the thing coming down. Chinese builds weather this way: 下雨 (to rain), 下雪 (to snow). There is no "it" in the sentence, so 下雨了 means "it has started raining", with 了 marking the change of state. To ask, say 下雨了吗. Keep 下雨, the event, apart from 雨, the noun: 今天有大雨 means heavy rain is expected.
The story behind the character
下
The mirror image of 上. A line with a short mark below it. Xu Shen wrote 下, 底也: "down, the bottom." Another indicated direction, plain as can be.
雨
A line of cloud on top, drops falling below. Xu Shen put it the plainest way possible: 雨, 水从云下也: "rain, water coming down from clouds." When you write 雨, you're drawing a cloud that's raining.